Tuesday, July 4, 2017

This is Kind of Sad. Astronomers Find a Failed Star Orbiting a Dead Star

This is Kind of Sad. Astronomers Find a Failed Star Orbiting a Dead Star:

Death is simply a part of life, and this is no less the case where stars and other astronomical objects are concerned. Sure, the timelines are much, much greater where these are concerned, but the basic rule is the same. Much like all living organism, stars eventually reach old age and become white dwarfs. And some are not even fortunate enough to be born, instead becoming a class of failed stars known as brown dwarfs.

Despite being familiar with these objects, astronomers were certainly not expecting to find examples of both in a single star system! And yet, according to a new study, that is precisely what an international team of astronomers discovered when looked at WD 1202-024. Using data from the Kepler space telescope, they spotted a binary system consisting of a failed star (a brown dwarf) and the remnant of a star (a white dwarf).

The team which made the discovery consisted of researchers from the Kavli Institute for Astrophysics and Space Research at MIT, the Harvard-Smithsonian Center for Astrophysics (CfA), the Exoplanet Research Institute (iREx) and NASA’s Ames Research Center. The study that describes their findings, titled “WD 1202-024: The Shortest-Period Pre-Cataclysmic Variable“, was recently published in the Monthly Notices of the Royal Astronomical Society.





Artist’s impression of a T-type brown dwarf. Credit: Tyrogthekreeper under a Wikimedia Commons Attribution-Share Alike 3.0 Unported license
Originally, the white dwarf was identified by the Sloan Digital Sky Survey (SDSS) – designated as WD1202-024 – and was thought to be a solitary star. However, while examining the light-curves of stars that had been surveyed by the K2 mission, Dr. Saul Rappaport (M.I.T.) and Andrew Vanderburg (of the CfA) – the lead author and a co-authors on the study, respectively – noted a curious drop in its brightness.

Whereas the transits of exoplanets are known to cause small dips in brightness, the light curve in this case showed particularly deep and broad eclipses. In addition, between these eclipses, there were changes in brightness which appeared to be due to the cool component (i.e. the brown dwarf) being illuminated by the much hotter white dwarf. This too was unexpected, as it indicated that the transiting object was rather large.

To get to the bottom of this, the team devised a model based on data obtained from K2 mission, the SDSS survey and the Magellan 6.5-m telescope. They also used data from five different ground-based telescopes on three continents, which included amateur-operated 36-cm and 80-cm telescopes in Arizona, the 1-m telescope at the South African Astronomical Observatory, and the 1.6-m telescope at Mont-Megantic Observatory (‘OMM’) in Quebec.

From this combined data, they were able to deduce that their observations were consistent with a hot white dwarf of 0.4 Solar masses being eclipsed by brown dwarf companion of 0.067 Solar masses. They also determined that these two objects, which are seen nearly edge-on, orbited each other with a period of just 71 minutes and 12 seconds – which works out to a speed of about 100 km/s.





The lightcurve picked up by the K2 mission (black line), with a geometrical model to emulate an illumination effect on the companion star (red line), while the blue line is the fit to the model based on the length of the K2 observations.. Credit: UBishop
But as Lorne Nelson – a professor at Bishop’s University and one of the co-authors on the paper – explained, the team also wanted to address how this system came to be. “We had constructed a robust model but we still had to address the ‘big-picture’ issues such as how this system formed and what would be its ultimate fate,” he said.

To do this, they used sophisticated computer models to simulate the formation and evolution of WD1202. According to their scenario, the primordial system consisted of a 1.25 Solar mass star and a brown dwarf that were in a 150 day orbit with each other. As the star aged, it began to expand, becoming a red giant that eventually pulled its brown dwarf companion into a much tighter orbit.

They also constructed a 3-D animation to illustrate the effect this had. As Nelson described it:

“It is similar to an egg-beater effect. The brown dwarf spirals in towards the center of the red giant and causes most of the mass of the red giant to be lifted off of the core and to be expelled. The result is a brown dwarf in an extraordinarily tight, short-period orbit with the hot helium core of the giant. That core then cools and becomes the white dwarf that we observe today.”
In addition, their calculations showed that the primordial binary must have formed about 3 billion years ago, and that in less than 250 million years, the white dwarf will begin cannibalizing the brown dwarf. At this point, the brown dwarf is likely to be pulled apart and form a circumstellar disk around the white dwarf, which it will slowly accrete material from.





Artist’s impression of the star in its multi-million year long and previously unobservable phase as a large, red supergiant. Credit: CAASTRO / Mats Björklund (Magipics)
When this happens, the binary will begin showing the signs of a cataclysmic variable (CV), which include a flickering lightcurve. And in the end, it is likely that the entire system will go out in a fiery cataclysm – aka. a type 1a supernova. It should also be noted that this 250 year period is the shortest pre-cataclysmic variable of any binary system ever discovered, making this find even more of a rarity.

So perhaps the find was not so sad after all. Yes, a failed star is orbiting a star in its death throes, but its important to remember they were not always this way. At one time, WD 1202-024 was a vital star that was orbited by a super-heavy gas giant. Only in approaching death did the two become so tight in their orbits, and the perfect picture of failed stardom and near-stellar-death. And in time, they will come together to produce a cataclysmic explosion. I think we can all agree, its best to go out with a bang!

The findings of this study were presented at a press conference last week (on Tuesday, June 6th, 2017) at the 230th Meeting of the American Astronomical Society.

Further Reading: Bishop’s University, MNRAS

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The Corona Borealis Constellation

The Corona Borealis Constellation:

Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at the “Northern Crown” – the Corona Borealis constellation. Enjoy!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.

One of these constellations was Corona Borealis, otherwise known as the “Northern Crown”. This small, faint constellation is the counterpart to Corona Australis – aka. the “Southern Crown”. It is bordered by the constellations of Hercules, Boötes and Serpens Caput, and has gone on to become one of the 88 modern constellations recognized by the International Astronomical Union.

Name and Meaning:

In mythology, Corona Borealis was supposed to represent the crown worn by Ariadne – a present from Dionysus. In Celtic lore, it was known as Caer Arianrhod, or the “Castle of the Silver Circle”, home to the Lady Arianrhod. Oddly enough, it was also known to the Native Americans as well, who referred to it as the “Camp Circle” – a heavenly rendition of their celestial ancestors.





Hercules and Corona Borealis, as depicted in Urania’s Mirror (c.?1825). Credit: Library of Congress

History of Observation:

Corona Borealis was one of the original 48 constellations mentioned in the Almagest by Ptolemy. To the medieval Arab astronomers, the constellation was known as al-Fakkah,  which means “separated” or “broken up” a reference to the resemblance of the constellation’s stars to a loose string of jewels (sometimes portrayed as a broken dish). The name was later Latinized as Alphecca, which was later given to Alpha Coronae Borealis. In 1920, it was adopted by the International Astronomical Union (IAU) as one of the 88 modern constellations.

Notable Objects:

Corona Borealis has no bright stars, 6 main stars and 24 stellar members with Bayer/Flamsteed designations. It’s brightest star – Alpha Coronae Borealis (Alphecca) – is an eclipsing binary located about 75 light years away. The primary components is a white main sequence star that is believed to have a large disc around it (as evidenced by the amount of infrared radiation it emits), and may even have a planetary or proto-planetary system.

The second brightest star, Beta Coronae Borealis (Nusakan), is a spectroscopic binary that is located 114 light years away. It is an Alpha-2 Canum Venaticorum (ACV) type star, a class of variable (named after a star in the constellation Canes Venatici) that are main sequence stars that are chemically peculiar and have strong magnetic fields. Its traditional name, Nusakan, comes from the Arabic an-nasaqan which means “the (two) series.”





Corona Borealis Galaxy Cluster – Abell 2065. Credit: NASA (Wikisky)
Corona Borealis contains few Deep Sky Objects that would be visible to amateur astronomers. The most notable is the Corona Borealis Galaxy Cluster (aka. Abell 2065), a densely-populated cluster located between 1 and 1.5 billion years from Earth. It lies about one degree southwest of Beta Coronae Borealis, in the southwest corner of the constellation. The cluster contains more than 400 galaxies in an area spanning about one degree in the sky.

Corona Borealis also has five stars that have confirmed exoplanets orbiting them, most of which were detected using the radial velocity method. These include the the orange giant Epsilon Coronae Borealis, which has a Super-Jupiter (6.7 Jupiter masses) that orbits it at a distance of 1.3 AU and with a period of 418 days.

There’s also Kappa Coronae Borealis, an orange subgiant that is orbited by both a debris disk and a gas giant. This planet is 2.5 times as massive as Jupiter and orbits the star with a period of 3.4 years. Omicron Coronae Borealis is a clump giant (a type of red giant) with one confirmed exoplanet – a gas giant with 0.83 Jupiter masses that orbits its star every 187 days.

HD 145457 is an orange giant that has one confirmed planet of 2.9 Jupiter masses that takes 176 days to complete an orbit. XO-1 is a yellow main-sequence star located approximately 560 light-years away with a hot Jupiter (roughly the same size as Jupiter) exoplanet. This planet was discovered using the transit method and completes an orbit around its star every three days.





Artist’s concept of “hot Jupiter” orbiting a distant star. Credit: NASA/JPL-Caltech

Finding Corona Borealis:

Corona Borealis is visible at latitudes between +90° and -50° and is best seen at culmination during the month of July. Using binoculars, let’s start with Alpha Coronae Borealis. It’s name is Gemma, or on some star charts – Alphecca. At 75 light years away, we have a nice binary star system whose companion star produces a very faint eclipse every 17.3599 days. Even though Gemma is quite some distance in relative sky terms from Ursa Major, you might be surprised to know that it’s actually part of the Ursa Major moving star group!

Shift your attention to Beta Coronae Borealis. It’s traditional name Nusakan. Again, it looks like one star, but it’s actually two. Nusakan is a double star that’s about 114 light-years and the primary is a variable star that changes every so slightly about every 41 days. The two components are separated by about 0.25 arc seconds – way too close for amateur telescopes – but that’s not all. In 1944 F.J. Neubauer found a small variation in the radial velocity of Nusakan which may lead to a third orbiting body about 10 times the size of Jupiter.

Now have a look at Gamma. Again, we have a binary star that’s just too darn close to split with anything but a large telescope. Struve 1967 is a close binary with an orbit of 91 years. The position angle is 265º and separation about 0.2″. Instead, try focusing your attention on Zeta 1 and Zeta 2. Known as Struve 1965, this pair is a pretty blue white and they are well spaced at 7.03″ and about one stellar magnitude in difference. Nu1 and Nu2 are also very pretty in binoculars. Here we have an optic double star. Although they aren’t physically related, this widely seperated pair of orange giant stars is a pleasing sight in binoculars!





The location of the Corona Borealis Constellation. Credit: IAU/Sky&Telescope magazine
Out of all the singular stars here, you definitely have to take a look at R Coronae Borelis – known as R Cor Bor. Discovered nearly 200 years ago by English amateur, Edward Pigot, R Coronae Borealis is the prototype star of the R Coronae Borealis (RCB) type variables. They are very unusual type of variable star – one where the variability is caused by the formation of a cloud of carbon dust in the line of sight. Near the stellar photosphere, a cloud is formed – dimming the star’s visual brightness by several magnitudes.

Then the cloud dissipates as it moves away from the star. All RCB types are hydrogen-poor, carbon- and helium-rich, and high-luminosity. They are simultaneously eruptive and pulsating. They could fade anywhere from 1 to 9 magnitudes in a month… Or in a hundred days. It’s normally magnitude 6… But it could be magnitude 14. No wonder it has the nickname “Fade-Out star,” or “Reverse Nova”!

Unfortunately, Corona Borealis contains no bright deep sky objects, but it does have one claim to fame – the highly concentrated galaxy cluster, Abell 2065. For observers with larger telescope, many members of this fascinating 1-1.5 billion light years distant group are visible. This rich cluster of galaxies is located slightly more than a degree southwest of Beta Cor Bor and covers about a full degree of sky! Not for the faint of heart… Some of these galaxies list at magnitude 18….

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

Sources:

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Gravitational Astronomy? How Detecting Gravitational Waves Changes Everything

Gravitational Astronomy? How Detecting Gravitational Waves Changes Everything:



Just a couple of weeks ago, astronomers from Caltech announced their third detection of gravitational waves from the Laser Interferometer Gravitational-Wave Observatory or LIGO.

As with the previous two detections, astronomers have determined that the waves were generated when two intermediate-mass black holes slammed into each other, sending out ripples of distorted spacetime.

One black hole had 31.2 times the mass of the Sun, while the other had 19.4 solar masses. The two spiraled inward towards each other, until they merged into a single black hole with 48.7 solar masses. And if you do the math, twice the mass of the Sun was converted into gravitational waves as the black holes merged.

On January 4th, 2017, LIGO detected two black holes merging into one. Courtesy Caltech/MIT/LIGO Laboratory
These gravitational waves traveled outward from the colossal collision at the speed of light, stretching and compressing spacetime like a tsunami wave crossing the ocean until they reached Earth, located about 2.9 billion light-years away.

The waves swept past each of the two LIGO facilities, located in different parts of the United States, stretching the length of carefully calibrated laser measurements. And from this, researchers were able to detect the direction, distance and strength of the original merger.

Seriously, if this isn’t one of the coolest things you’ve ever heard, I’m clearly easily impressed.

Now that the third detection has been made, I think it’s safe to say we’re entering a brand new field of gravitational astronomy. In the coming decades, astronomers will use gravitational waves to peer into regions they could never see before.

Being able to perceive gravitational waves is like getting a whole new sense. It’s like having eyes and then suddenly getting the ability to perceive sound.

This whole new science will take decades to unlock, and we’re just getting started.

As Einstein predicted, any mass moving through space generates ripples in spacetime. When you’re just walking along, you’re actually generating tiny ripples. If you can detect these ripples, you can work backwards to figure out what size of mass made the ripples, what direction it was moving, etc.

Even in places that you couldn’t see in any other way. Let me give you a couple of examples.

Black holes, obviously, are the low hanging fruit. When they’re not actively feeding, they’re completely invisible, only detectable by how they gravitational attract objects or bend light from objects passing behind them.

But seen in gravitational waves, they’re like ships moving across the ocean, leaving ripples of distorted spacetime behind them.

With our current capabilities through LIGO, astronomers can only detect the most massive objects moving at a significant portion of the speed of light. A regular black hole merger doesn’t do the trick – there’s not enough mass. Even a supermassive black hole merger isn’t detectable yet because these mergers seem to happen too slowly.

LIGO has already significantly increased the number of black holes with known masses. The observatory has definitively detected two sets of black hole mergers (bright blue). For each event, LIGO determined the individual masses of the black holes before they merged, as well as the mass of the black hole produced by the merger. The black holes shown with a dotted border represent a LIGO candidate event that was too weak to be conclusively claimed as a detection. Credit: LIGO/Caltech/Sonoma State (Aurore Simonnet)
This is why all the detections so far have been intermediate-mass black holes with dozens of times the mass of our Sun. And we can only detect them at the moment that they’re merging together, when they’re generating the most intense gravitational waves.

If we can boost the sensitivity of our gravitational wave detectors, we should be able to spot mergers of less and more massive black holes.

But merging isn’t the only thing they do. Black holes are born when stars with many more times the mass of our Sun collapse in on themselves and explode as supernovae. Some stars, we’ve now learned just implode as black holes, never generating the supernovae, so this process happens entirely hidden from us.

Is there a singularity at the center of a black hole event horizon, or is there something there, some kind of object smaller than a neutron star, but bigger than an infinitely small point? As black holes merge together, we could see beyond the event horizon with gravitational waves, mapping out the invisible region within to get a sense of what’s going on down there.

This illustration shows the merger of two black holes and the gravitational waves that ripple outward as the black holes spiral toward each other. In reality, the area near the black holes would appear highly warped, and the gravitational waves would be difficult to see directly. Credit: LIGO/T. Pyle
We want to know about even less massive objects like neutron stars, which can also form from a supernova explosion. These neutron stars can orbit one another and merge generating some of the most powerful explosions in the Universe: gamma ray bursts. But do neutron stars have surface features? Different densities? Could we detect a wobble in the gravitational waves in the last moments before a merger?

And not everything needs to merge. Sensitive gravitational wave detectors could sense binary objects with a large imbalance, like a black hole or neutron star orbiting around a main sequence star. We could detect future mergers by their gravitational waves.

Are gravitational waves a momentary distortion of spacetime, or do they leave some kind of permanent dent on the Universe that we could trace back? Will we see echoes of gravity from gravitational waves reflecting and refracting through the fabric of the cosmos?

Perhaps the greatest challenge will be using gravitational waves to see beyond the Cosmic Microwave Background Radiation. This region shows us the Universe 380,000 years after the Big Bang, when everything was cool enough for light to move freely through the Universe.

But there was mass there, before that moment. Moving, merging mass that would have generated gravitational waves. As we explained in a previous article, astronomers are working to find the imprint of these gravitational waves on the Cosmic Microwave Background, like an echo, or a shadow. Perhaps there’s a deeper Cosmic Gravitational Background Radiation out there, one which will let us see right to the beginning of time, just moments after the Big Bang.

And as always, there will be the surprises. The discoveries in this new field that nobody ever saw coming. The “that’s funny” moments that take researchers down into whole new fields of discovery, and new insights into how the Universe works.

The Laser Interferometer Gravitational-Wave Observatory (LIGO)facility in Livingston, Louisiana. The other facility is located in Hanford, Washington. Image: LIGO
The Laser Interferometer Gravitational-Wave Observatory (LIGO) facility in Livingston, Louisiana. The other facility is located in Hanford, Washington. Image: LIGO
The LIGO project was begun back in 1994, and the first iteration operated from 2002 to 2012 without a single gravitational wave detection. It was clear that the facility wasn’t sensitive enough, so researchers went back and made massive improvements.

In 2008, they started improving the facility, and in 2015, Advanced LIGO came online with much more sensitivity. With the increased capabilities, Advanced LIGO made its first discovery in 2016, and now two more discoveries have been added.

LIGO can currently only detect the general hemisphere of the sky where a gravitational wave was emitted. And so, LIGO’s next improvement will be to add another facility in India, called INDIGO. In addition to improving the sensitivity of LIGO, this will give astronomers three observations of each event, to precisely detect the origin of the gravitational waves. Then visual astronomers could do follow up observations, to map the event to anything in other wavelengths.

Current operating facilities in the global network include the twin LIGO detectors—in Hanford, Washington, and Livingston, Louisiana—and GEO600 in Germany. The Virgo detector in Italy and the Kamioka Gravitational Wave Detector (KAGRA) in Japan are undergoing upgrades and are expected to begin operations in 2016 and 2018, respectively. A sixth observatory is being planned in India. Having more gravitational-wave observatories around the globe helps scientists pin down the locations and sources of gravitational waves coming from space. Image made in February 2016. Credit: Caltech/MIT/LIGO Lab
A European experiment known as Virgo has been operating for a few years as well, agreeing to collaborate with the LIGO team if any detections are made. So far, the Virgo experiment hasn’t found anything, but it’s being upgraded with 10 times the sensitivity, which should be fully operational by 2018.

A Japanese experiment called the Kamioka Gravitational Wave Detector, or KAGRA, will come online in 2018 as well, and be able to contribute to the observations. It should be capable of detecting binary neutron star mergers out to nearly a billion light-years away.

Just with visual astronomy, there are a set of next generation supergravitational wave telescopes in the works, which should come online in the next few decades.

The Europeans are building the Einstein Telescope, which will have detection arms 10 km long, compared to 4 km for LIGO. That’s like, 6 more km.

There’s the European Space Agency’s space-based Laser Interferometer Space Antenna, or LISA, which could launch in 2030. This will consist of a fleet of 3 spacecraft which will maintain a precise distance of 2.5 million km from each other. Compare that to the Earth-based detection distances, and you can see why the future of observations will come from space.

The Laser Interferometer Space Antenna (LISA) consists of three spacecraft orbiting the sun in a triangular configuration. Credit: NASA
And that last idea, looking right back to the beginning of time could be a possibility with the Big Bang Observer mission, which will have a fleet of 12 spacecraft flying in formation. This is still all in the proposal stage, so no concrete date for if or when they’ll actually fly.

Gravitational wave astronomy is one of the most exciting fields of astronomy. This entirely new sense is pushing out our understanding of the cosmos in entirely new directions, allowing us to see regions we could never even imagine exploring before. I can’t wait to see what happens next.

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NASA Announces 10, That’s Right 10! New Planets in Their Star’s Habitable Zone

NASA Announces 10, That’s Right 10! New Planets in Their Star’s Habitable Zone:

The Kepler space telescope is surely the gift that keeps on giving. After being deployed in 2009, it went on to detect a total of 2,335 confirmed exoplanets and 582 multi-planet systems. Even after two of its reaction wheels failed, it carried on with its K2 mission, which has discovered an additional 520 candidates, 148 of which have been confirmed. And with yet another extension, which will last beyond 2018, it shows no signs of stopping!

In the most recent catalog to be released by the Kepler mission, an additional 219 new planet candidates have been added to its database. More significantly, 10 of these planets were found to be terrestrial (i.e. rocky), of comparable in size to Earth and orbited within their star’s habitable zone – the distance where surface temperatures would be warm enough to support liquid water.

These findings were presented at a news conference on Monday, June 19th, at NASA’s Ames Research Center. Of all the catalogs of Kepler candidates that have been released to date, this one is the most comprehensive and detailed. The eighth in a series of Kepler exoplanet catalogs, this one is based on data that was obtained from the first four years of the mission and is the final catalog that covers the spacecraft’s observations of the Cygnus constellation.





 Credits: NASA/Wendy Stenzel
Since 2014, Kepler has ceased looking at a set starfield in the Cygnus constellation and has been collecting data on its second mission – observing fields on the plane of the ecliptic of the Milky Way Galaxy. With the release of this catalog, there are now 4,034 planet candidates that have been identified by Kepler – of which 2,335 have been verified.

An important aspect of this catalog were the methods that were used for producing it, which were the most sophisticated to date. As with all planets detected by Kepler, the latest finds were all made using the transit method. This consists of monitoring stars for occasional dips in brightness, which is used to confirm the presence of planets transiting between the star and the observer.

To ensure that the detections in this latest catalog were real, the team relied on two approaches to eliminate false positives. This consisted of introducing simulated transits into the dataset to make sure the dips that Kepler detected were consistent with planets. Then, they added false signals to see how often the analysis mistook these for planet transits. From this, they were able to tell which planets were overcounted and which were undercounted.

This led to another exciting find, which was the indication that for all of the smaller exoplanets discovered by Kepler, most fell within one of two distinct groupings. Essentially, half the planets that we know of in the galaxy are either rocky in nature and larger than Earth (i.e. Super-Earth’s), or are gas giants that are comparable in size to Neptune (i.e. smaller gas giants).



This conclusion was reached by a team of researchers who used the W.M. Keck Observatory to measure the sizes of 1,300 stars in the Kepler field of view. From this, they were able to determine the radii of 2,000 Kepler planets with extreme precision, and found that there was a clear division between rocky, Earth-sized planets and gaseous planets smaller than Neptune – with few in between.

As Benjamin Fulton, a doctoral candidate at the University of Hawaii in Manoa and the lead author of this study, explained:

“We like to think of this study as classifying planets in the same way that biologists identify new species of animals. Finding two distinct groups of exoplanets is like discovering mammals and lizards make up distinct branches of a family tree.”
These results are sure to have drastic implications when it comes to knowing the frequency of different types of planets in our galaxy, as well as the study of planet formation. For instance, they noted that most rocky planets discovered by Kepler are up to 75% larger than Earth. And for reasons that are not yet clear, about half of them take on hydrogen and helium, which swells their size to the point that they become almost Neptune-sized.





Histogram shows the number of planets per 100 stars as a function of planet size relative to Earth. Credits: NASA/Ames Research Center/CalTech/University of Hawaii/B.J. Fulton
These findings could similarly have significant implications in the search for habitable planets and extra-terrestrial life. As Mario Perez, Kepler program scientist in the Astrophysics Division of NASA’s Science Mission Directorate, said during the presentation:

“The Kepler data set is unique, as it is the only one containing a population of these near Earth-analogs – planets with roughly the same size and orbit as Earth. Understanding their frequency in the galaxy will help inform the design of future NASA missions to directly image another Earth.”
From this information, scientists will be able to know with a greater degree of certainty just how many “Earth-like” planets exist within our galaxy. The most recent estimates place the number of planets in the Milky Way at about 100 billion. And based on this data, it would seem that many of these are similar in composition to Earth, albeit larger.

Combined with a statistical models of how many of these can be found within a circumstellar habitable zone, we should have a better idea of just how many potentially-life-bearing worlds are out there. If nothing else, this should simplify some of the math in the Drake Equation!

In the meantime, the Kepler space telescope will continue to make observations of nearby star systems in order to learn more about their exoplanets. This includes the TRAPPIST-1 system and its seven Earth-sized, rocky planets. Its a safe bet that before it is finally retired after 2018, it will have some more surprises in store for us!

Further Reading: NASA, NASA Kepler and K2

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Messier 49 – the NGC 4472 Elliptical Galaxy

Messier 49 – the NGC 4472 Elliptical Galaxy:

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at Orion’s Nebula’s “little brother”, the De Marian’s Nebula!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is the elliptical galaxy known as Messier 49 (aka. NGC 4472). Located in the southern skies in the constellation of Virgo, this galaxy is one several members of the Virgo Cluster of galaxies and is located 55.9 million light years from Earth. On a clear night, and allowing for good light conditions, it can be seen with binoculars or a small telescope, and will appear as a hazy patch in the sky.

Description:

Messier 49 is the brightest of the Virgo Cluster member galaxies, which is pretty accurate considering it’s only about 60 million light years away and may span an area as large as 160,000 light years. It is a huge system of globular clusters, much less concentrated than Virgo cluster member M87 – but a giant none the less. As Stephen E. Zep (et al) wrote in a 2000 study:

“We present new radial velocities for 87 globular clusters around the elliptical galaxy NGC 4472 and combine these with our previously published data to create a data set of velocities for 144 globular clusters around NGC 4472. We utilize this data set to analyze the kinematics of the NGC 4472 globular cluster system. The new data confirm our previous discovery that the metal-poor clusters have significantly higher velocity dispersion than the metal-rich clusters in NGC 4472. The very small angular momentum in the metal-rich population requires efficient angular momentum transport during the formation of this population, which is spatially concentrated and chemically enriched. Such angular momentum transfer can be provided by galaxy mergers, but it has not been achieved in other extant models of elliptical galaxy formation that include dark matter halos. We also calculate the velocity dispersion as a function of radius and show that it is consistent with roughly isotropic orbits for the clusters and the mass distribution of NGC 4472 inferred from X-ray observations of the hot gas around the galaxy.”




This ground-based image shows the Small Magellanic Cloud. The area of the SMIDGE survey is highlighted, as well as the position of NGC 248. Credit: NASA/ESA/Hubble/Digitized Sky Survey 2
However, there was something going on in the mass structure of M49 that astronomers were curious about… Something they couldn’t quite explain. Was it dark matter? As M. Lowenstein wrote in a 1992 study:

“An attempt to constrain the total mass distribution of the well-observed giant elliptical galaxy NGC 4472 is realized by constructing simultaneous equilibrium models for the gas and stars using all available relevant optical and X-ray data. The value of <?>, the emission-weighted average value of kT, derived from the Ginga spectrum, <?> = 1.9 ± 0.2 keV, can be reproduced only in hydrostatic models where nonluminous matter comprises at least 90% of the total mass. However, in general, these mass models are not consistent with observed projected stellar and globular cluster velocity dispersions at moderate radii.”
The next thing you know, nuclear outburst were discovered – the product of interaction with a neighboring galaxy. As B. Biller (et al) indicated in a 2004 study:

“We present the analysis of the Chandra ACIS observations of the giant elliptical galaxy NGC 4472. The Chandra Observatory’s arcsec resolution reveals a number of new features. Specifically: 1) an ~8 arc min streamer or arm (this corresponds to a linear size of 36 kpc) extending southwest of the galaxy and an assymetrical, somewhat truncated streamer to the northeast. Smaller, morphologically similar structures are observed in NGC 4636 and are explained as shocks from a nuclear outburst in the recent past. The larger size of the NGC 4472 streamers requires a correspondingly higher energy input compared to the NGC 4636 case. The asymmetry of the streamers may be due to the interaction of NGC 4472 with the ambient Virgo cluster gas. 2) A string of small, extended sources south of the nucleus. These sources may stem from an interaction of NGC 4472 with the galaxy UGC 7637. 3) X-ray cavities corresponding to radio lobes, where expanding radio plasma has evacuated the X-ray emitting gas. We also present a luminosity function for the X-ray point sources detected within NGC 4472 which we compare to that for other early type galaxies.”




Chandra images showing 4 of the 9 galaxies discovered (left), and an artist’s impression on showing how gas falls towards a black hole and becomes a rapidly spinning disk of matter near the center (right). Credit: NASA/Chandra
But the very best was yet to come… the discovery of a black hole! According to NASA, the results from NASA’s Chandra X-ray Observatory, combined with new theoretical calculations, provide one of the best pieces of evidence yet that many supermassive black holes are spinning extremely rapidly. The images on the left show 4 out of the 9 large galaxies included in the Chandra study, each containing a supermassive black hole in its center.

The Chandra images show pairs of huge bubbles, or cavities, in the hot gaseous atmospheres of the galaxies, created in each case by jets produced by a central supermassive black hole. Studying these cavities allows the power output of the jets to be calculated. This sets constraints on the spin of the black holes when combined with theoretical models. The Chandra images were also used to estimate how much fuel is available for each supermassive black hole, using a simple model for the way matter falls towards such an object.

The artist’s impression on the right side of the main graphic shows gas within a “sphere of influence” falling straight inwards towards a black hole before joining a rapidly spinning disk of matter near the center. Most of the material in this disk is swallowed by the black hole, but some of it is swept outwards in jets (colored blue) by quickly spinning magnetic fields close to the black hole.

Previous work with these Chandra data showed that the higher the rate at which matter falls towards these supermassive black holes, the higher their power output is in jets. However, without detailed theory the implications of this result for black hole behavior were unclear. The new study uses these Chandra results combined with leading theoretical models for the production of jets, plus general relativity, to show that the supermassive black holes in these galaxies must be spinning at close to the maximum rate. If black holes are spinning at this limit, material can be dragged around them at close to the speed of light, the speed limit from Einstein’s theory of relativity.





Atlas Image obtained of Messier 49, taken by the Two Micron All Sky Survey (2MASS). Credit: NASA/UofMass/IPAC/Caltech/NASA/NSF/2MASS

History of Observation:

According to SEDS, M49 was the first member of the Virgo cluster of galaxies to be discovered, by Charles Messier, who cataloged it on February 19th, 1771. As he recorded in his notes at the time:

“Nebula discovered near the star Rho Virginis. One cannot see it without difficulty with an ordinary telescope of 3.5-feet [FL]. The Comet of 1779 was compared by M. Messier with this nebula on April 22 and 23: The comet and the nebula had the same light. M. Messier has reported this nebula on the chart of the route of the comet, which appeared in the volume of the Academy of the same year 1779. Seen again on April 10, 1781.” Eight years later, on April 22, 1779, on the occasion of following the comet of that year, and on the hunt for finding more nebulous objects in competition to other observers, Barnabas Oriani independently rediscovered this ‘nebula’: “Very pale and looking exactly like the comet [1779 Bode, C/1779 A1].”
In his Bedford Catalogue of 1844, Admiral William H. Smyth confused this finding with Messier’s discovery:

“A bright, round, and well-defined nebula, on the Virgin’s left shoulder; exactly on the line between Delta Virginis and Beta Leonis, 8deg, or less than half-way, from the former star. With an eyepiece magnifying 93 times, there are only two telescopic stars in the field, one of which is in the sp and the other in the sf quadrant; and the nebula has a very pearly aspect. This object was discovered by Oriani in 1771 [this is wrong: it was Messier who discovered it that year; Oriani found it only in 1779], and registered by Messier as a “faint nebula, not seen without difficulty,” with a telescope of 3 1/2 feet in length. It is a pity that this active and very assiduous astronomer could not have been furnished with one of the giant telescopes of the present days. Had he possessed efficient means, there can be no doubt of the augmentation of his useful and, in its day, unique Catalogue: a collection of objects for which sidereal astronomy must ever remain indebted to him.” This error was repeated by John Herschel in his General Catalogue of 1864 (GC), who also erroneously assigned this object to “1771 Oriani,” and also found its way into J.L.E. Dreyer’s NGC.
Let’s hope you don’t mistake it with the many other galaxies nearby!





The location of Messier 49 within the Virgo constellation. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Locating Messier 49:

Galaxy hopping isn’t an easy chore and it takes some practice. Starting looking for M49 about halfway between Epsilon and Beta Virginis. Use Gamma to help triangulate your position. At near magnitude 8, Messier 49 is quite binocular possible and would show under dark sky conditions as a faint, very small egg shaped fog. However, it will not show in a finderscope of a telescope – but the nearby stars will.

Use their patterns to help guide you there. Because galaxies require dark skies, M49 cannot be found under urban conditions or during moonlit nights. In telescopes as small as 70mm, it will appear as a nebulous egg shape and become brighter – but no more resolved to larger instruments. To assist in location, begin with lowest magnification and increase magnification once found to darken background field.

And here are the quick facts to help you get started!

Object Name: Messier 49
Alternative Designations: M49, NGC 4472
Object Type: Elliptical Galaxy
Constellation: Virgo
Right Ascension: 12 : 29.8 (h:m)
Declination: +08 : 00 (deg:m)
Distance: 60000 (kly)
Visual Brightness: 8.4 (mag)
Apparent Dimension: 9×7.5 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

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How Far Does Light Travel in a Year?

How Far Does Light Travel in a Year?:

The Universe is an extremely big place. As astronomers looked farther into space over the centuries, and deeper into the past, they came to understand just how small and insignificant our planet and our species seem by comparison. At the same time, ongoing investigations into electromagnetism and distant stars led scientists to deduce what the the speed of light is – and that it is the fastest speed obtainable.

As such, astronomers have taken to using the the distance light travels within a single year (aka. a light year) to measure distances on the interstellar and intergalactic scale. But how far does light travel in a year? Basically, it moves at a speed of 299,792,458 meters per second (1080 million km/hour; 671 million mph), which works out to about 9,460.5 billion km (5,878.5 billion miles) per year.

The Speed of Light:

Calculating the speed of light has been a preoccupation for scientists for many centuries. And prior to the 17th century, there was disagreement over whether the speed of light was finite, or if it moved from one spot to the next instantaneously. In 1676, Danish astronomer Ole Romer settled the argument when his observations of the apparent motion of Jupiter’s moon Io revealed that the speed of light was finite.





Light moves at different wavelengths, represented here by the different colors seen in a prism. Credit: NASA/ESA
From his observations, fellow Danish astronomer Christiaan Huygens calculated the speed of light at 220,000 km/s (136,701 mi/s). Over the course of the nest two centuries, the speed of light was refined further and further, producing estimates that ranged from about 299,000 to 315,000 km/s (185,790 to 195,732 mi/s).

This was followed by James Clerk Maxwell, who proposed in 1865 that light was an electromagnetic wave. In his theory of electromagnetism, the speed of light was represented as c. And then in 1905, Albert Einstein proposed his theory of Special Relativity, which postulated that the speed of light (c) was constant, regardless of the inertial reference frame of the observer or the motion of the light source.

By 1975, after centuries of refined measurements, the speed of light in a vacuum was calculated at 299,792,458 meters per second. Ongoing research also revealed that light travels at different wavelengths and is made up of subatomic particles known as photons, which have no mass and behave as both particles and waves.

Light-Year:

As already noted, the speed of light (expressed in meters per second) means that light travels a distance of 9,460,528,000,000 km (or 5,878,499,817,000 miles) in a single year. This distance is known as a “light year”, and is used to measure objects in the Universe that are at a considerable distances from us.





Examples of objects in our Universe, and the scale of their distances, based on the light year as a standard measure. Credit: Bob King.
For example, the nearest star to Earth (Proxima Centauri) is roughly 4.22 light-years distant. The center of the Milky Way Galaxy is 26,000 light-years away, while the nearest large galaxy (Andromeda) is 2.5 million light-years away. To date, the candidate for the farthest galaxy from Earth is MACS0647-JD, which is located approximately 13.3 billion light years away.

And the Cosmic Microwave Background, the relic radiation which is believed to be leftover from the Big Bang, is located some 13.8 billion light years away. The discovery of this radiation not only bolstered the Big Bang Theory, but also gave astronomers an accurate assessment of the age of the Universe. This brings up another important point about measuring cosmic distances in light years, which is the fact that space and time are intertwined.

You see, when we see the light coming from a distant object, we’re actually looking back in time. When we see the light from a star located 400 light-years away, we’re actually seeing light that was emitted from the star 400 years ago. Hence, we’re seeing the star as it looked 400 years ago, not as it appears today. As a result, looking at objects billions of light-years from Earth is to see billions of light-years back in time.

Yes, light travels at an extremely fast speed. But given the sheer size and scale of the Universe, it can still take billions of years from certain points in the Universe to reach us here on Earth. Hence why knowing how long it takes for light to travel a single year is so useful to scientists. Not only does it allow us to comprehend the scale of the Universe, it also allows us to chart the process of cosmic evolution.

We have written many articles about the speed of light here at Universe Today. Here’s How Far is a Light Year?, What is the Speed of Light?, How Much Stuff is in a Light Year?, How Does Light Travel?, and How Far Can You See in the Universe?

Want more info on light-years? Here’s an article about light-years for HowStuffWorks, and here’s an answer from PhysLink.

We’ve also recorded an episode of Astronomy Cast on this topic. Listen here, Episode 10: Measuring Distance in the Universe.

Sources:

The post How Far Does Light Travel in a Year? appeared first on Universe Today.

How Does Mercury Compare to Earth?

How Does Mercury Compare to Earth?:

Mercury was appropriately named after the Roman messenger of the Gods. This is owed to the fact that its apparent motion in the night sky was faster than that of any of the other planets. As astronomers learned more about this “messenger planet”, they came to understand that its motion was due to its close orbit to the Sun, which causes it to complete a single orbit every 88 days.

Mercury’s proximity to the Sun is merely one of its defining characteristics. Compared to the other planets of the Solar System, it experiences severe temperature variations, going from very hot to very cold. It’s also very rocky, and has no atmosphere to speak of. But to truly get a sense of how Mercury stacks up compared to the other planets of the Solar System, we need to a look at how Mercury compares to Earth.

Size, Mass and Orbit:

The diameter of Mercury is 4,879 km, which is approximately 38% the diameter of Earth. In other words, if you put three Mercurys side by side, they would be a little larger than the Earth from end to end. While this makes Mercury smaller than the largest natural satellites in our system – such as Ganymede and Titan – it is more massive and far more dense than they are.





Mercury, as imaged by the MESSENGER spacecraft, revealing parts of the never seen by human eyes. Image Credit: NASA/JHUAPL/Carnegie Institution of Washington
In fact, Mercury’s mass is approximately 3.3 x 1023 kg (5.5% the mass of Earth) which means that its density – at 5.427 g/cm3 – is the second highest of any planet in the Solar System, only slightly less than Earth’s (5.515 g/cm3). This also means that Mercury’s surface gravity is 3.7 m/s2, which is the equivalent of 38% of Earth’s gravity (0.38 g). This means that if you weighed 100 kg (220 lbs) on Earth, you would weigh 38 kg (84 lbs) on Mercury.

Meanwhile, the surface area of Mercury is 75 million square kilometers, which is approximately 10% the surface area of Earth. If you could unwrap Mercury, it would be almost twice the area of Asia (44 million square km). And the volume of Mercury is 6.1 x 1010 km3, which works out to 5.4% the volume of Earth. In other words, you could fit Mercury inside Earth 18 times over and still have a bit of room to spare.

In terms of orbit, Mercury and Earth probably could not be more different. For one, Mercury has the most eccentric orbit of any planet in the Solar System (0.205), compared to Earth’s 0.0167. Because of this, its distance from the Sun varies between 46 million km (29 million mi) at its closest (perihelion) to 70 million km (43 million mi) at its farthest (aphelion).

This puts Mercury much closer to the Sun than Earth, which orbits at an average distance of 149,598,023 km (92,955,902 mi), or 1 AU. This distance ranges from 147,095,000 km (91,401,000 mi) to 152,100,000 km (94,500,000 mi) – 0.98 to 1.017 AU. And with an average orbital velocity of 47.362 km/s (29.429 mi/s), it takes Mercury a total 87.969 Earth days to complete a single orbit – compared to Earth’s 365.25 days.





The Orbit of Mercury during the year 2006. Credit: Wikipedia Commons/Eurocommuter
However, since Mercury also takes 58.646 days to complete a single rotation, it takes 176 Earth days for the Sun to return to the same place in the sky (aka. a solar day). So on Mercury, a single day is twice as long as a single year. Meanwhile on Earth, a single solar day is 24 hours long, owing to its rapid rotation of 1674.4 km/h. Mercury also has the lowest axial tilt of any planet in the Solar System – approximately 0.027°, compared to Earth’s 23.439°.

Structure and Composition:

Much like Earth, Mercury is a terrestrial planet, which means it is composed of silicate minerals and metals that are differentiated between a solid metal core and a silicate crust and mantle. For Mercury, the breakdown of these elements is higher than Earth. Whereas Earth is primarily composed of silicate minerals, Mercury is composed of 70% metallic and 30% of silicate materials.

Also like Earth, Mercury’s interior is believed to be composed of a molten iron that is surrounded by a mantle of silicate material. Mercury’s core, mantle and crust measure 1,800 km, 600 km, and 100-300 km thick, respectively; while Earth’s core, mantle and crust measure 3478 km, 2800 km, and up to 100 km thick, respectively.

What’s more, geologists estimate that Mercury’s core occupies about 42% of its volume (compared to Earth’s 17%) and the core has a higher iron content than that of any other major planet in the Solar System. Several theories have been proposed to explain this, the most widely accepted being that Mercury was once a larger planet that was struck by a planetesimal that stripped away much of the original crust and mantle.





Internal structure of Mercury: 1. Crust: 100–300 km thick 2. Mantle: 600 km thick 3. Core: 1,800 km radius. Credit: MASA/JPL

Surface Features:

In terms of its surface, Mercury is much more like the Moon than Earth. It has a dry landscape pockmarked by asteroid impact craters and ancient lava flows. Combined with extensive plains, these indicate that the planet has been geologically inactive for billions of years.

Names for these features come from a variety of sources. Craters are named for artists, musicians, painters, and authors; ridges are named for scientists; depressions are named after works of architecture; mountains are named for the word “hot” in different languages; planes are named for Mercury in various languages; escarpments are named for ships of scientific expeditions, and valleys are named after radio telescope facilities.

During and following its formation 4.6 billion years ago, Mercury was heavily bombarded by comets and asteroids, and perhaps again during the Late Heavy Bombardment period. Due to its lack of an atmosphere and precipitation, these craters remain intact billions of years later. Craters on Mercury range in diameter from small bowl-shaped cavities to multi-ringed impact basins hundreds of kilometers across.

The largest known crater is Caloris Basin, which measures 1,550 km (963 mi) in diameter. The impact that created it was so powerful that it caused lava eruptions on the other side of the planet and left a concentric ring over 2 km (1.24 mi) tall surrounding the impact crater. Overall, about 15 impact basins have been identified on those parts of Mercury that have been surveyed.





Enhanced-color image of Munch, Sander and Poe craters amid volcanic plains (orange) near Caloris Basin. Credit: NASA/JHUAPL/Carnegie Institution of Washington
Earth’s surface, meanwhile, is significantly different. For starters, 70% of the surface is covered in oceans while the areas where the Earth’s crust rises above sea level forms the continents. Both above and below sea level, there are mountainous features, volcanoes, scarps (trenches), canyons, plateaus, and abyssal plains. The remaining portions of the surface are covered by mountains, deserts, plains, plateaus, and other landforms.

Mercury’s surface shows many signs of being geologically active in the past, mainly in the form of narrow ridges that extend up to hundreds of kilometers in length. It is believed that these were formed as Mercury’s core and mantle cooled and contracted at a time when the crust had already solidified. However, geological activity ceased billions of years ago and its crust has been solid ever since.

Meanwhile, Earth is still geologically active, owning to convection of the mantle. The lithosphere (the crust and upper layer of the mantle) is broken into pieces called tectonic plates. These plates move in relation to one another and interactions between them is what causes earthquakes, volcanic activity (such as the “Pacific Ring of Fire“), mountain-building, and oceanic trench formation.

Atmosphere and Temperature:

When it comes to their atmospheres, Earth and Mercury could not be more different. Earth has a dense atmosphere composed of five main layers – the Troposphere, the Stratosphere, the Mesosphere, the Thermosphere, and the Exosphere. Earth’s atmosphere is also primarily composed of nitrogen (78%) and oxygen (21%) with trace concentrations of water vapor, carbon dioxide, and other gaseous molecules.





The Fast Imaging Plasma Spectrometer on board MESSENGER has found that the solar wind is able to bear down on Mercury enough to blast particles from its surface into its wispy atmosphere. Credit: Shannon Kohlitz, Media Academica, LLC
Because of this, the average surface temperature on Earth is approximately 14°C, with plenty of variation due to geographical region, elevation, and time of year. The hottest temperature ever recorded on Earth was 70.7°C (159°F) in the Lut Desert of Iran, while the coldest temperature was -89.2°C (-129°F) at the Soviet Vostok Station on the Antarctic Plateau.

Mercury, meanwhile, has a tenuous and variable exosphere that is made up of hydrogen, helium, oxygen, sodium, calcium, potassium and water vapor, with a combined pressure level of about 10-14 bar (one-quadrillionth of Earth’s atmospheric pressure). It is believed this exosphere was formed from particles captured from the Sun, volcanic outgassing and debris kicked into orbit by micrometeorite impacts.

Because it lacks a viable atmosphere, Mercury has no way to retain the heat from the Sun. As a result of this and its high eccentricity, the planet experiences far more extreme variations in temperature than Earth does. Whereas the side that faces the Sun can reach temperatures of up to 700 K (427° C), the side that is in darkness can reach temperatures as low as 100 K (-173° C).

Despite these highs in temperature, the existence of water ice and even organic molecules has been confirmed on Mercury’s surface. The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below the planetary average. In this respect, Mercury and Earth have something else in common, which is the presence of water ice in its polar regions.





Mercury’s Magnetic Field. Credit: NASA

Magnetic Fields:

Much like Earth, Mercury has a significant, and apparently global, magnetic field, one which is about 1.1% the strength of Earth’s. It is likely that this magnetic field is generated by a dynamo effect, in a manner similar to the magnetic field of Earth. This dynamo effect would result from the circulation of the planet’s iron-rich liquid core.

Mercury’s magnetic field is strong enough to deflect the solar wind around the planet, thus creating a magnetosphere. The planet’s magnetosphere, though small enough to fit within Earth, is strong enough to trap solar wind plasma, which contributes to the space weathering of the planet’s surface.

All told, Mercury and Earth are in stark contrast. While both are terrestrial in nature, Mercury is significantly smaller and less massive than Earth, though it has a similar density. Mercury’s composition is also much more metallic than that of Earth, and its 3:2 orbital resonance results in a single day being twice as long as a year.

But perhaps most stark of all are the extremes in temperature variations that Mercury goes through compared to Earth. Naturally, this is due to the fact that Mercury orbits much closer to the Sun than the Earth does and has no atmosphere to speak of. And its long days and long nights also mean that one side is constantly being baked by the Sun, or in freezing darkness.

We have written many stories about Mercury on Universe Today. Here’s Interesting Facts About Mercury, What Type of Planet is Mercury?, How Long is a Day on Mercury?, The Orbit of Mercury. How Long is a Year on Mercury?, What is the Surface Temperature of Mercury?, Water Ice and Organics Found at Mercury’s North Pole, Characteristics of Mercury,, Surface of Mercury, and Missions to Mercury

If you’d like more information on Mercury, check out NASA’s Solar System Exploration Guide, and here’s a link to NASA’s MESSENGER Misson Page.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Mercury. Listen to it here, Episode 49: Mercury.

Sources:

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Wednesday, June 28, 2017

Super-Earth Planet Found in the Habitable Zone of a Nearby Star

Super-Earth Planet Found in the Habitable Zone of a Nearby Star:

M-type stars, also known as “red dwarfs”, have become a popular target for exoplanet hunters of late. This is understandable given the sheer number of terrestrial (i.e. rocky) planets that have been discovered orbiting around red dwarf stars in recent years. These discoveries include the closest exoplanet to our Solar System (Proxima b) and the seven planets discovered around TRAPPIST-1, three of which orbit within the star’s habitable zone.

The latest find comes from a team of international astronomers who discovered a planet around GJ 625, a red dwarf star located just 21 light years away from Earth. This terrestrial planet is roughly 2.82 times the mass of Earth (aka. a “super-Earth”) and orbits within the star’s habitable zone. Once again, news of this discovery is prompting questions about whether or not this world could indeed be habitable (and also inhabited).

The international team was led by Alejandro Mascareño of the Canary Islands Institute of Astrophysics (IAC), and includes members from the University of La Laguna and the University of Geneva. Their research was also supported by the Spanish National Research Council (CSIS), the Institute of Space Studies of Catalonia (IEEC), and the National Institute For Astrophysics (INAF).





Diagram showing GJ 625’s habitable zone in comparison’s to the Sun’s. Credit: IAC
The study which details their findings was recently accepted for publication by the journal Astronomy & Astrophysics, and appears online under the title “A super-Earth on the Inner Edge of the Habitable Zone of the Nearby M-dwarf GJ 625“. According to the study, the team used radial-velocity measurements of GJ 625 in order to determine the presence of a planet that has between two and three times the mass of Earth.

This discovery was part of the HArps-n red Dwarf Exoplanet Survey (HADES), which studies red dwarf stars to determine the presence of potentially habitable planets orbiting them. This survey relies on the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) instrument – which is part of the 3.6-meter Galileo National Telescope (TNG) at the IAC’s Roque de Los Muchachos Observatory on the island of La Palma.

Using this instrument, the team collected high-resolution spectroscopic data of the GJ 625 system over the course of three years. Specifically, they measured small variations in the stars radial velocity, which are attributed to the gravitational pull of a planet. From a total of 151 spectra obtained, they were able to determine that the planet (GJ 625 b) was likely terrestrial and had a minimum mass of 2.82 ± 0.51 Earth masses.

Moreover, they obtained distance estimates that placed it roughly 0.078 AU from its star, and an orbital period estimate of 14.628 ± 0.013 days. At this distance, the planet’s orbit places it just within GJ 625’s habitable zone. Of course, this does not mean conclusively that the planet has conditions conducive to life on its surface, but it is an encouraging indication.





Tjhe Observatorio del Roque de los Muchachos, located on the island of La Palma. Credit: IAC
As Alejandro Suárez Mascareño explained in an IAC press release:

“As GJ 625 is a relatively cool star the planet is situated at the edge of its habitability zone, in which liquid water can exist on its surface. In fact, depending on the cloud cover of its atmosphere and on its rotation, it could potentially be habitable”.
This is not the first time that the HADES project detected an exoplanet around a red dwarf star. In fact, back in 2016, a team of international researchers used this project to discover 2 super-Earths orbiting GJ 3998, a red dwarf located about 58 ± 2.28 light years from Earth. Beyond HADES, this discovery is yet another in a long line of rocky exoplanets that have been discovered in the habitable zone of a nearby red dwarf star.

Such findings are very encouraging since red dwarfs are the most common type of star in the known Universe- accounting for an estimated 70% of stars in our galaxy alone. Combined with the fact that they can exist for up to 10 trillion years, red dwarf systems are considered a prime candidate in the search for habitable exoplanets.

But as with all other planets discovered around red dwarf stars, there are unresolved questions about how the star’s variability and stability could affect the planet. For starters, red dwarf stars are known to vary in brightness and periodically release gigantic flares. In addition, any planet close enough to be within the star’s habitable zone would likely be tidally-locked with it, meaning that one side would be exposed to a considerable amount of radiation.





Artist’s impression of of the exoplanets orbiting a red dwarf star. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).
As such, additional observations will need to be made of this exoplanet candidate using the time-tested transit method. According to Jonay Hernández – a professor from the University of La Laguna, a researcher with the IAC and one of the co-authors on the study – future studies using this method will not only be able to confirm the planet’s existence and characterize it, but also determine if there are any other planets in the system.

“In the future, new observing campaigns of photometric observations will be essential to try to detect the transit of this planet across its star, given its proximity to the Sun,” he said. “There is a possibility that there are more rocky planets around GJ 625 in orbits which are nearer to, or further away from the star, and within the habitability zone, which we will keep on combing”.

According to Rafael Rebolo – one of the study’s co-authors from the Univeristy of La Laguna, a research with the IAC, and a member of the CSIS – future surveys using the transit method will also allow astronomers to determine with a fair degree of certainty whether or not GJ 625 b has the all-important ingredient for habitability – i.e. an atmosphere:

“The detection of a transit will allow us to determine its radius and its density, and will allow us to characterize its atmosphere by the transmitted light observe using high resolution high stability spectrographs on the GTC or on telescopes of the next generation in the northern hemisphere, such as the Thirty Meter Telescope (TMT)”.




Artist’s impression of a system of exoplanets orbiting a low mass, red dwarf star. Credit: NASA/JPL
But what is perhaps most exciting about this latest find is how it adds to the population of extra-solar planets within our cosmic neighborhood. Given their proximity, each of these planets represent a major opportunity for research. And as Dr. Mascareño told Universe Today via email:

“While we have already found more than 3600 extra-solar planets, the exoplanet population in our near neighborhood is still somewhat unknown. At 21 ly from the Sun, GJ 625 is one of the 100 nearest  stars, and right now GJ 625 b is one of the 30 nearest exoplanets detected and the 6th nearest potentially habitable exoplanet.”
Once again, ongoing surveys of nearby star systems is providing plenty of potential targets in the search for life beyond our Solar System. And with both ground-based and space-based next-generation telescopes joining the search, we can expect to find many, many more candidates in the coming years. In the meantime, be sure to check out this animation of GJ 625 b and its parent star:

Further Reading: arXiv, IAC

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