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Titan’s thick haze. Image: NASA/JPL/Space Science Institute.
Is the surf up yet on Titan? As the moon of Saturn moves towards northern summer, scientists are trying to spot signs of the winds picking up. This weekend, the Cassini spacecraft plans a look at the the largest body of liquid on Titan, Kraken Mare, to see if there are any waves on this huge hydrocarbon sea.
Cassini will make the 105th flyby of Titan on Monday (Sept. 22) to probe the moon’s atmosphere, seas and even a crater. The spacecraft will examine “the seas and lakes of the northern polar area, including Kraken and Ligeia at resolution better than 3 miles (5 kilometers) per pixel,” the Cassini website stated.
Besides wet areas of Titan, Cassini will also look at dunes and the relatively fresh-looking Sinlap crater, where scientists hope to get a high-resolution image. Managers also plan a mosaic of Tsegihi — a bright zone south of the equator — and the darker dune-filled area of Fensal. The spacecraft additionally will examine aerosols and the transparency of hazes in Titan’s atmosphere.
Titan is of interest to scientists in part because its chemistry is a possible precursor to what made life possible. Earlier this week, Cassini transmitted several raw images of its view of Titan and Saturn right now — some of the latest pictures are below.
A raw image of Saturn’s moon Titan taken by the Cassini spacecraft Sept. 14, 2014. Credit: NASA/JPL/Space Science Institute
Atmospheric features on Saturn’s moon Titan appear to be faintly visible in this raw image taken by the Cassini spacecraft Sept. 10, 2014. Credit: NASA/JPL/Space Science Institute
A crescent Titan beckons the Cassini spacecraft (in Saturn’s system) in this image taken Aug. 24, 2014. Credit: NASA/JPL/Space Science Institute
A raw image of Saturn taken by the Cassini spacecraft Sept. 15, 2014. Credit: NASA/JPL/Space Science Institute
Optical and X-ray images of the star WASP 18. X-ray Credit: NASA / CXC / SAO / I.Pillitteri et al; Optical Credit: DSS; Illustration Credit: NASA / CXC / M.Weiss
Hot young stars are wildly active, emitting huge eruptions of charged particles form their surfaces. But as they age they naturally become less active, their X-ray emission weakens and their rotation slows.
Astronomers have theorized that a hot Jupiter — a sizzling gas giant circling close to its host star — might be able to sustain a young star’s activity, ultimately prolonging its youth. Earlier this year, two astronomers from the Harvard-Smithsonian Center for Astrophysics tested this hypothesis and found it true.
But now, observations of a different system show the opposite effect: a planet that’s causing its star to age much more quickly.
The planet, WASP-18b has a mass roughly 10 times Jupiter’s and circles its host star in less than 23 hours. So it’s not exactly a classic hot Jupiter — a sizzling gas giant whipping around its host star — because it’s characteristics are a little more drastic.
“WASP-18b is an extreme exoplanet,” said lead author Ignazio Pillitteri of the National Institute for Astrophysics in Italy, in a news release. “It is one of the most massive hot Jupiters known and one of the closest to its host star, and these characteristics lead to unexpected behavior.”
The team thinks WASP-18 is 600 million years old, relatively young compared to our 5-billion-year-old Sun. But when Pillitteri and colleagues took a long look with NASA’s Chandra X-ray Observatory at the star, they didn’t see any X-rays — a telltale sign the star is youthful. In fact, the observations show the star is 100 times less active than it should be.
“We think the planet is aging the star by wreaking havoc on its innards,” said co-author Scott Wolk (who also worked on the previous study showing the opposite effect) from the Harvard-Smithsonian Center for Astrophysics.
The researchers argue that tidal forces created by the gravitational pull of the massive planet might have disrupted the star’s magnetic field generated by the motion of conductive plasma deep inside the star. It’s possible the exoplanet significantly interfered with the upper layers of the convective zone, reduced any mixing of stellar material, and effectively canceled out the magnetic activity.
The effect of tidal forces from the planet may also explain an unusually high amount of lithium seen in the star. Lithium is usually abundant in younger stars, but disappears over time as convection carries it further toward the star’s center, where it’s destroyed by nuclear reactions. So if there’s less convection — as seems to be the case for WASP 18 — then the lithium won’t circulate toward the center of the star and instead will survive.
The findings have been published in the July issue of Astronomy and Astrophysics and are available online.
Aurora over a Glacier Lagoon. Credit and copyright: James Woodend, UK
The winners of the 2014 “Astronomy Photographer of the Year” competition have been announced at the Royal Observatory in Greenwich England, and British photographer James Woodend’s gorgeous image of the aurora dancing across the Icelandic night sky was named the overall winner. This is the sixth year for the competition, which is run by the ROG and the Sky at Night Magazine.
“Every year the competition becomes more and more challenging to judge and we’re always astounded by the skill of the photographers,” said Dr. Maggie Aderin-Pocock, a presenter on The Sky at Night and one of the judges for the competition. “The Deep Space category, where the entrants have been able to capture such amazing details of objects light-years away and are almost on par with images taken by the Hubble Space Telescope, never fails to impress.”
See more gorgeous images and a list of the winners in the various categories below:
Earth and Space
James Woodend (UK) with Aurora over a Glacier Lagoon (Winner and Overall Winner) Matt James (Australia) with Wind Farm Star Trails (Runner-up) Patrick Cullis (USA) with Moon Balloon (Highly Commended) Catalin Beldea (Romania) with Totality from Above the Clouds (Highly Commended) O Chul Kwon (South Korea) with Venus-Lunar Occultation (Highly Commended)
Horsehead Nebula (IC 434). Credit and copyright: Bill Snyder, USA.
Deep Space
Bill Snyder (USA) with Horsehead Nebula (IC 434) (Winner) David Fitz-Henry (Australia) with The Helix Nebula (NGC 7293) (Runner-Up) J.P Metsävainio (Finland) with Veil Nebula Detail (IC 1340) (Highly Commended) Rogelio Bernal Andreo (USA) with California vs Pleiades (Highly Commended) Marco Lorenzi (China) with At the Feet of Orion (NGC 1999) – Full Field (Highly Commended)
Stunning closeup of our Sun, entitled ‘Ripples in a Pond.’ Credit and copyright: Alexandra Hart, UK
Our Solar System Alexandra Hart (UK) with Ripples in a Pond (Winner) George Tarsoudis (Greece) with Best of the Craters (Runner-Up) Alexandra Hart (UK) with Solar Nexus (Highly Commended) Stephen Ramsden (USA) with Calcium K Eruption (Highly Commended) Tunç Tezel (Turkey) with Diamond and Rubies (Highly Commended)
The Horsehead Nebula (IC 434). Credit and copyright: Shishir and Shashank Dholakia, USA, Aged 15.
Young Astronomy Photographer of the Year
Shishir & Shashank Dholakia (USA, aged 15) with The Horsehead Nebula (IC 434) (Winner) Emmett Sparling (Canada, aged 15) with New Year over Cypress Mountain (Runner-up) Olivia Williamson (UK, aged 10) with The Martian Territory (Highly Commended) Shishir & Shashank Dholakia (USA, aged 15) with The Heart Nebula (IC 1805) (Highly Commended) Emily Jeremy (UK, aged 12) with Moon Behind the Trees (Highly Commended)
Hybrid Solar Eclipse. Credit and copyright: Eugen Kamenew, Germany
Special Prize: People and Space Eugen Kamenew (Germany) with Hybrid Solar Eclipse 2 (Winner) Julie Fletcher (Australia) with Lost Souls (Runner-up)
Coastal Stairways. Credit and copyright: Chris Murphy, New Zealand
Special Prize: Sir Patrick Moore prize for Best Newcomer
Chris Murphy (New Zealand) with Coastal Stairways (Winner)
NGC 3718 via a robotic scope, Credit and copyright: Mark Hanson, USA
Robotic Scope Image of the Year
Mark Hanson (USA) with NGC 3718 (Winner)
For all the winners see the ROG website, and for other photos not shown here, you can see more at the Astronomy Photographer of the Year Flickr site . If you are in the UK, you can see an exhibition of the winning photos as the Astronomy Centre, Royal Observatory, Greenwich, from now until February 22, 2015.
Find more info at the ROG website, where you can also find info about the competition for next year — start planning ahead!
An artist concept of MAVEN in orbit around Mars. (Credit: NASA’s Goddard Spaceflight Center).
NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) orbiter is oh-so-close to its destination after a 10-month journey. It’s scheduled to arrive in orbit Sunday (Sept. 21) around 9:50 p.m. EDT (1:50 a.m. UTC) if all goes well, but there are a few things that need to happen, in order, first.
One big obstacle is already out of the way. MAVEN controllers had expected to do final engine burn tweaks to put it on the right trajectory, but the mission is so on-target that it won’t be needed.
“#MAVEN orbit insertion sequence has been activated on the s/c. No additional ground intervention is needed to enter #Mars’ orbit on Sunday,” the official account tweeted yesterday (Sept. 18).
So what does the sequence entail? MAVEN will need to turn on its six thruster engines for a 33-minute braking maneuver to slow it down. This will allow the gravity of Mars to “capture” the spacecraft into an elliptical or oval-shaped orbit.
Should that all go safely, MAVEN still has a lot of work to do before being ready to capture information about the upper atmosphere of the Red Planet. All spacecraft go through a commissioning phase to ensure their instruments are working correctly and that they are in the correct orbit and orientation to do observations.
Controllers are interested in learning about the comet and its effect on the upper atmosphere, so they will stop the commissioning to make those measurements. MAVEN will also be oriented in such a way that its solar panels are protected as much as possible from the dust, although scientists now believe the risk of strikes is very low.
This graphic depicts the orbit of comet C/2013 A1 Siding Spring as it swings around the sun in 2014. On Oct. 19, 2014 the comet will have a very close pass at Mars. Its nucleus will miss Mars by about 82,000 miles (132,000 kilometers). Credit: NASA/JPL-Caltech
MAVEN is expected to work at Mars for a year, but investigators are hoping it will be for longer so that the atmosphere can be tracked through more of a solar cycle. The Sun’s activity is a major influencer on the atmosphere and the “stripping” of molecules from it over time, which could have thinned Mars’ atmosphere in the ancient past.
The spacecraft will also serve as a backup communications and data relay for the Opportunity and Curiosity rovers on the surface, which might be needed if some of the older NASA Mars spacecraft that fulfill that function experience technical difficulties.
Some of the many thousands of merging galaxies identified within the GAMA survey. Credit: Professor Simon Driver and Dr Aaron Robotham, ICRAR.
The Anglo-Australian Telescope in New South Wales has been watching how lazy giant galaxies gain size – and it isn’t because they create their own stars. In a research project known as the Galaxy And Mass Assembly (GAMA) survey, a group of Australian scientists led by Professor Simon Driver at the International Centre for Radio Astronomy Research (ICRAR) have found the Universe’s most massive galaxies prefer “eating” their neighbors.
According to findings published in the journal “Monthly Notices of the Royal Astronomical Society”, astronomers studied more than 22,000 individual galaxies to see how they grew. Apparently smaller galaxies are exceptional star producers, forming their stellar members from their own gases. However, larger galaxies are lazy. They aren’t very good at stellar creation. These massive monsters rarely produce new stars on their own. So how do they grow? They cannibalize their companions. Dr. Aaron Robotham, who is based at the University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR), explains that smaller ‘dwarf’ galaxies were being consumed by their heavyweight peers.
“All galaxies start off small and grow by collecting gas and quite efficiently turning it into stars,” he said. “Then every now and then they get completely cannibalized by some much larger galaxy.”
So how does our home galaxy stack up to these findings? Dr. Robotham, who led the research, said the Milky Way is at a tipping point and is expected to now grow mainly by eating smaller galaxies, rather than by collecting gas.
“The Milky Way hasn’t merged with another large galaxy for a long time but you can still see remnants of all the old galaxies we’ve cannibalized,” he said. “We’re also going to eat two nearby dwarf galaxies, the Large and Small Magellanic Clouds, in about four billion years.” Robotham also added the Milky Way wouldn’t escape unscathed. Eventually, in about five billion years, we’ll encounter the nearby Andromeda Galaxy and the tables will be turned. “Technically, Andromeda will eat us because it’s the more massive one,” he said.
This simulation shows what will happen when the Milky Way and Andromeda get closer together and then collide, and then finally come together once more to merge into an even bigger galaxy.
Simulation Credit: Prof Chris Power (ICRAR-UWA), Dr Alex Hobbs (ETH Zurich), Prof Justin Reid (University of Surrey), Dr Dave Cole (University of Central Lancashire) and the Theoretical Astrophysics Group at the University of Leicester. Video Production Credit: Pete Wheeler, ICRAR.
What exactly is going on here? Is it a case of mutual attraction? According to Dr. Robotham when galaxies grow, they acquire a heavy-duty gravitational field allowing them to suck in neighboring galaxies with ease. But why do they stop producing their own stars? Is it because they have exhausted their fuel? Robotham said star formation slow downs in really massive galaxies might be “because of extreme feedback events in a very bright region at the center of a galaxy known as an active galactic nucleus.”
“The topic is much debated, but a popular mechanism is where the active galactic nucleus basically cooks the gas and prevents it from cooling down to form stars,” Dr. Robotham said.
Will the entire Universe one day become just a single, large galaxy? In reality, gravity may very well cause galaxies groups and clusters to congeal into a limited number of super-giant galaxies, but that will take many billions of years to occur.
“If you waited a really, really, really long time that would eventually happen, but by really long I mean many times the age of the Universe so far,” Dr. Robotham said.
While the GAMA survey findings didn’t take billions of years, it didn’t happen overnight either. It took seven years and more than 90 scientists to complete – and it wasn’t a single revelation. From this work there have been over 60 publications and there are still another 180 in progress!
Artist’s conception of the New Horizons spacecraft flying past Pluto and Charon, one of the dwarf planet’s moons. Credit: Johns Hopkins University/APL
Here’s Hydra! The New Horizons team spotted the tiny moon of Pluto in July, about six months ahead of when they expected to. You can check it out in the images below. The find is exciting in itself, but it also bodes well for the spacecraft’s search for orbital debris to prepare for its close encounter with the system in July 2015.
Most of Pluto’s moons were discovered while New Horizons was under development, or already on its way. Mission planners are thus concerned that there could be moons out there that aren’t discovered yet — moons that could pose a danger to the spacecraft if it ended up in the wrong spot at the wrong time. That’s why the team is engaging in long-range views to see what else is lurking in Pluto’s vicinity.
“We’re thrilled to see it, because it shows that our satellite-search techniques work, and that our camera is operating superbly. But it’s also exciting just to see a third member of the Pluto system come into view, as proof that we’re almost there,” stated science team member John Spencer, of the Southwest Research Institute.
Watch the difference: Pluto’s moon Hydra stands out in these images taken by the New Horizons spacecraft on July 18 and 20, 2014. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Hydra was spotted using the spacecraft’s Long Range Reconnaissance Imager (LORRI), which took 48 images of 10 seconds apiece between July 18 and July 20. Then the team used half the images, the ones that show Hydra better, to create the images you see above.
The spacecraft was still 267 million miles (430 million kilometers) from Pluto when the images were taken. Another moon discovered around the same time as Hydra — Nix — is still too close to be seen given it’s so close to Pluto, but just wait.
Meanwhile, scientists are busily trying to figure out where to send New Horizons after Pluto. In July, researchers using the Hubble Space Telescope began a full-scale search for a suitable Kuiper Belt Object, which would be one of trillions of icy or rocky objects beyond Neptune’s orbit. Flying past a KBO would provide more clues as to how the Solar System formed, since these objects are considered leftovers of the chunks of matter that came together to form the planets.
Enigmatic Uranus as seen through the automated eyes of Voyager 2 in 1986. (Credit: NASA/JPL).
It’s no joke… now is the time to begin searching the much-maligned (and mispronounced) planet Uranus as it reaches opposition in early October leading up to a very special celestial event.
Last month, we looked at the challenges of spying the solar system’s outermost ice giant world, Neptune. Currently located in the adjacent constellation Aquarius, Neptune is now 39 degrees from Uranus and widening. The two worlds had a close conjunction of just over one degree of separation in late 1993, and only long time observers of the distant worlds remember a time waaaay back in the early-1970s where the two worlds appeared farther apart than 2014 as seen from our Earthly vantage point.
Uranus rising to the east the evening of October 7th, just prior to the start of the October 8th lunar eclipse later the same evening. Created using Stellarium.
In 2014, opposition occurs at 21:00 Universal Time (UT)/5:00 PM EDT on October 7th. If this date sounds familiar, it’s because Full Moon and the second total lunar eclipse of 2014 and the ongoing lunar tetrad of eclipses occurs less than 24 hours afterwards. This puts Uranus extremely close to the eclipsed Moon, and a remote slice of the high Arctic will actually see the Moon occult (pass in front of) Uranus during totality. Such a coincidence is extremely rare: the last time the Moon occulted a naked eye planet during totality occurred back during Shakespearian times in 1591, when Saturn was covered by the eclipsed Moon. This close conjunction as seen from English soil possibly by the bard himself was mentioned in David Levy’s book and doctoral thesis The Sky in Early Modern English Literature, and a similar event involving Saturn occurs in 2344 AD.
The footprint of the October 8th occultation of Uranus. Credit: Occult 4.1.
We’re also in a cycle of occultations of Uranus in 2014, as the speedy Moon slides in front of the slow moving world every lunation until December 2015. Oppositions of Uranus — actually pronounced “YOOR-un-us” so as not to rhyme with a bodily orifice — currently occur in the month of September and move forward across our calendar by about 4 days a year.
Uranus (lower left) near the limb of the gibbous Moon of September 11th, 2014. Credit: Roger Hutchinson.
This year sees Uranus in the astronomical constellation Pisces just south of the March equinoctial point. Uranus is moving towards and will pass within a degree of the +5.7 magnitude star 96 Piscium in late October through early November. Shining at magnitude +5.7 through the opposition season, Uranus presents a disk 3.7” in size at the telescope. You can get a positive ID on the planet by patiently sweeping the field of view: Uranus is the tiny blue-green “dot” that, unlike a star, refuses to come into a pinpoint focus.
The apparent path of Uranus from September 2014 through January 2015 across the constellation Pisces. The inset shows the tilt and orbit of its major moons across a 2′ field of view. Created by the author using Starry Night Education software.
Uranus also presents us with one of the key mysteries of the solar system. Namely, what’s up with its 97.8 degree rotational tilt? Clearly, the world sustained a major blow sometime in the solar system’s early history. In 2014, we’re viewing the world at about a 28 degree tilt and widening. This will continue until we’re looking straight at the south pole of Uranus in early 2030s. Of course, “south” and “north” are pretty arbitrary when you’re knocked back over 90 degrees on your axis! And while we enjoy the September Equinox next week on September 23rd, the last equinox for any would-be “Uranians” occurred on December 16th, 2007. This put the orbit of its moons edge-on from our point of view from 2006-2009 for only the third time since discovery of the planet in 1781. This won’t occur again until around 2049. Uranus also passed aphelion in 2009, which means it’s still at the farther end of its 19.1 to 17.3 astronomical unit (A.U.) range from the Sun in its 84 year orbit.
The moons of Uranus and Neptune as imaged during the 2011 opposition season. Credit: Rolf Wahl Olsen, used with permission.
And as often as Uranus ends up as the butt (bad pun) of many a scatological punch line, we can at least be glad that the world didn’t get named Georgium Sidus (Latin for “George’s Star”) after William Herschel’s benefactor, King George the III. Yes, this was a serious proposal (!). Herschel initially thought he’d found a comet upon spying Uranus, until he realized its slow motion implied a large object orbiting far out in the solar system.
A replica of the reflecting telescope that Herschel used to discover Uranus. Credit: Alun Salt/Wikimedia Commons image under a Creative Commons Attribution Share-Alike 2.0 license.
Spurious sightings of Uranus actually crop up on star maps prior to Herschel’s time, and in theory, it hovers juuusst above naked eye visibility near opposition as seen from a dark sky site… can you pick out Uranus without optical assistance during totality next month? Hershel and Lassell also made claims of spotting early ring systems around both Uranus and Neptune, though the true discovery of a tenuous ring system of Uranus was made by the Kuiper Airborne Observatory (a forerunner of SOFIA) during an occultation of a background star in 1977.
A corkscrew chart for the moons of Uranus through October. Credit: Ed Kotapish/Rings PDS node.
Looking for something more? Owners of large light buckets can capture and even image (see above) 5 of the 27 known moons of Uranus. We charted the orbital elongations for favorable apparitions through October 2014 (to the left). Check out last year’s chart for magnitudes, periods, and maximum separations for each respective moon. An occulting bar eyepiece may help you in your quest to cut down the ‘glare’ of nearby Uranus.
When will we return to Uranus? Thus far, humanity has explored the world up close exactly once, when Voyager 2 passed by in 1986. A possible “Uranus Probe” (perhaps, Uranus Orbiter is a better term) similar to Cassini has been an on- and off- proposal over the years, though it’d be a tough sell in the current era of ever dwindling budgets. Plutonium, a mandatory power source for deep space missions, is also in short supply. Such a mission might take up to a decade to enter orbit around Uranus, and would represent the farthest orbital reconnaissance of a world in our solar system. Speedy New Horizons is just whizzing by Pluto next July.
All great thoughts to ponder as you scour the skies for Uranus in the coming weeks!
Artist’s conception of a supermassive black hole in a galaxy’s center. Credit: NASA/JPL-Caltech
In a finding that could turn supermassive black hole formation theories upside-down, astronomers have spotted one of these beasts inside a tiny galaxy just 157 light-years across — about 500 times smaller than the Milky Way.
The clincher will be if the team can find more black holes like it, and that’s something they’re already starting to work on after the discovery inside of galaxy M60-UCD1. The ultracompact galaxy is one of only about 50 known to astronomers in the nearest galaxy clusters.
“It’s very much like a pinprick in the sky,” said lead researcher Anil Seth, an astrophysicist at the University of Utah, of M60-UCD1 during an online press briefing Tuesday (Sept. 16).
Seth said he realized something special was happening when he saw the plot for stellar motions inside of M60-UCD1, based on data from the Gemini North Telescope in Hawaii. The stars in the center of the galaxy were orbiting much more rapidly than those at the edge. The velocity was unexpected given the kind of stars that are in the galaxy.
“Immediately when I saw the stellar motions map, I knew we were seeing something exciting,” Seth said. “I knew pretty much right away there was an interesting result there.”
Ultracompact dwarf galaxy M60-UCD1 shines in the inset image based on images from the Hubble Space Telescope and Chandra X-Ray Telescope. Chandra data is pink, and Hubble data is red, green and blue. The large galaxy dominating the field of view is M60. At the right edge is NGC 4647. Credit: X-ray: NASA/CXC/MSU/J.Strader et al, Optical: NASA/STScI
In its weight class, M60-UCD1 is a standout. Last year, Seth was second co-author on a group that announced that it was the densest nearby galaxy, with stars jam-packed 25 times closer than in the Milky Way. It’s also one of the brightest they know of, a fact that is helped by the galaxy’s relative closeness to Earth. It’s roughly 54 million light-years away, as is the massive galaxy it orbits: M60. The two galaxies are only 20,000 light-years apart.
Supermassive black holes are known to lurk in the centers of most larger galaxies, including the Milky Way. How they got there in the first place, however, is unclear. The find inside of M60-UCD1 is especially intriguing given the relative size of the black hole to the galaxy itself. The black hole is about 15% of the galaxy’s mass, with an equivalent mass of 21 million Suns. The Milky Way’s black hole, by contrast, takes up less than a percentage of our galaxy’s mass.
Given so few ultracompact galaxies are known to astronomers, some basic properties are a mystery. For example, the mass of these galaxy types tends to be higher than expected based on their starlight.
Some astronomers suggest it’s because they have more massive stars than other galaxy types, but Seth said measurements of stars within M60-UCD1 (based on their orbital motion) show normal masses. The extra mass instead comes from the black hole, he argues, and that will likely be true of other ultracompact galaxies as well.
A Hubble Space Telescope image of ultracompact galaxy M60-UCD1 (inset), which is suspected to host a supermassive black hole at its center. It is orbiting the nearby massive galaxy M60. Within the same field of view is NGC 4647. Credit: NASA/Space Telescope Science Institute/European Space Agency
“It’s a new place to look for black holes that was previously not recognized,” he said, but acknowledged the idea of black holes existing in similar galaxies will not be widely accepted until the team makes more finds. An alternative explanation to a black hole could be a suite of low-mass stars or neutron stars that do not give off a lot of light, but Seth said the number of these required in M60-UCD1 is “unreasonably high.”
His team plans to look at several other ultracompact galaxies such as M60-UCD1, but perhaps only seven to eight others would be bright enough from Earth to perform these measurements, he said. (Further work would likely require an instrument such as the forthcoming Thirty-Meter Telescope, he said.) Additionally, Seth has research interests in globular clusters — vast collections of stars — and plans a visit to Hawaii next month to search for black holes in these objects as well.
Results were published today (Sept. 17) in the journal Nature.
Artist’s conception of the NASA Dawn spacecraft approaching Ceres. Credit: NASA
NASA’s Dawn spacecraft experienced technical problems in the past week that will force it to arrive at dwarf planet Ceres one month later than planned, the agency said in a statement yesterday (Sept. 16).
Controllers discovered Dawn was in safe mode Sept. 11 after radiation disabled its ion engine, which uses electrical fields to “push” the spacecraft along. The radiation stopped all engine thrusting activities. The thrusting resumed Monday (Sept. 15) after controllers identified and fixed the problem, but then they found another anomaly troubling the spacecraft.
Dawn’s main antenna was also disabled, forcing the spacecraft to send signals to Earth (a 53-minute roundtrip by light speed) through a weaker secondary antenna and slowing communications. The cause of this problem hasn’t been figured out yet, but controllers suspect radiation affected the computer’s software. A computer reset has solved the issue, NASA added. The spacecraft is now functioning normally.
Vesta (left) and Ceres. Vesta was photographed up close by the Dawn spacecraft from July 2011-Sept. 2012, while the best views we have to date of Ceres come from the Hubble Space Telescope. The bright white spot is still a mystery. Credit: NASA
“As a result of the change in the thrust plan, Dawn will enter into orbit around dwarf planet Ceres in April 2015, about a month later than previously planned. The plans for exploring Ceres once the spacecraft is in orbit, however, are not affected,” NASA’s Jet Propulsion Laboratory stated in a press release.
Dawn is en route to Ceres after orbiting the huge asteroid Vesta between July 2011 and September 2012. A similar suspected radiation blast three years ago also disabled Dawn’s engine before it reached Vesta, but the ion system worked perfectly in moving Dawn away from Vesta when that phase of its mission was complete, NASA noted.
Among Dawn’s findings at Vesta is that the asteroid is full of hydrogen, and it contains the hydrated mineral hydroxyl. This likely came to the asteroid when smaller space rocks brought the volatiles to its surface through low-speed collisions.
Spacecraft can experience radiation through energy from the Sun (particularly from solar flares) and also from cosmic rays, which are electrically charged particles that originate outside the Solar System. Earth’s atmosphere shields the surface from most space-based radiation.
This is the remnant of Kepler's supernova, the famous explosion that was discovered by Johannes Kepler in 1604. The red, green and blue colors show low, intermediate and high energy X-rays observed with NASA's Chandra X-ray Observatory, and the star field is from the Digitized Sky Survey.
As reported in our press release, a new study has used Chandra to identify what triggered this explosion. It had already been shown that the type of explosion was a so-called Type Ia supernova, the thermonuclear explosion of a white dwarf star. These supernovas are important cosmic distance markers for tracking the accelerated expansion of the Universe.
However, there is an ongoing controversy about Type Ia supernovas. Are they caused by a white dwarf pulling so much material from a companion star that it becomes unstable and explodes? Or do they result from the merger of two white dwarfs?
The new Chandra analysis shows that the Kepler supernova was triggered by an interaction between a white dwarf and a red giant star. The crucial evidence from Chandra was a disk-shaped structure near the center of the remnant. The researchers interpret this X-ray emission to be caused by the collision between supernova debris and disk-shaped material that the giant star expelled before the explosion. Another possibility was that the structure is just debris from the explosion.
The collapse of a massive star in a supernova explosion is an epic event. In less than a second a neutron star (or in some cases a black hole) is formed and the implosion is reversed, releasing prodigious amounts of light that can outshine billions of Suns. That is a spectacular way to be born. Here, I'll explain that the properties of neutron stars are no less spectacular, even though they are not as famous as their collapsed cousins, black holes.
Because of the incredible pressures involved in core collapse, the density of neutron stars is astounding: all of humanity could be squashed down to a sugar cube-sized piece of neutron star. The escape velocity from their surface is over half the speed of light but an approaching rocket ship would be stretched, then crushed and assimilated into the surface of the star in a moment. Resistance would be futile.
If this cricket ball were made of neutron star material it would weigh about 20 trillion kg, or about 40 times the estimated weight of the entire human population.
Another remarkable property is that neutron stars generate the most extreme magnetic fields known in the universe, up to a quadrillion times the strength of Earth's magnetic field. If one of these ultra-magnetic neutron stars, called a magnetar, flew past Earth within 100,000 miles, its magnetic field would destroy the data on every credit card on Earth. Luckily for our economy none are that close, but the distant ones can put on spectacular shows. In 2004 a magnetar underwent an extraordinary outburst and become one of the brightest objects ever observed in the sky, causing a disturbance in the Earth's ionosphere that was recorded around the globe, as described in this paper by astrophysicist Bryan Gaensler (@SciBry on Twitter) from the University of Sydney (my alma mater). That's impressive for an object about the size of a city that is located around 50 thousand light years away.
An artist's conception of the spectacular outburst from the magnetar SGR 1806-20, including magnetic field lines. After the initial flash, smaller pulsations in the data suggest hot spots on the rotating magnetar’s surface. This animation contains no audio, because "in space no-one can hear you scream". Credit: NASA
Neutron star behavior can be so odd and distinctive that their discovery was initially greeted as the possible discovery of extraterrestrial intelligence. The real explanation is that a pulsar, a rotating neutron star, was discovered. Pulsars have become such an important tool for physics research that two different Nobel Prizes have been awarded in their name, the first for their discovery by Antony Hewish. Many people - including myself - have argued that Jocelyn Bell Burnell should have been awarded part of the Nobel prize with Hewish, since she made the discovery, but in an expression of modesty or Imposter Syndrome, Bell Burnell later commented that she did not deserve the award. However, this does not diminish the significance of her discovery, and of the outstanding research that it enabled.
Jocelyn Bell Burnell with the radio telescope she used to discover pulsars. Credit:Jocelyn Bell Burnell.
The second Nobel prize was for Russell Hulse and Joseph Taylor, who discovered the first known binary pulsar, PSR1913+16, which has become extremely valuable for testing Einstein's Theory of General Relativity (GR). Since then other important objects have been discovered, including a double pulsar system known as PSR J0737-3039A/B that is one of the best objects available for testing GR and alternative theories of gravity, as explained in this paper by Michael Kramer from the University of Manchester.
Looking ahead in pulsar work, there is an exciting and ingenious project called the North American Nanohertz Observatory (NANOGrav) that is attempting a direct detection of gravitational waves, ripples in the fabric of space-time, using pulsars. Like several of the topics covered here this project deserves a dedicated blog post, but for now I'll just say that exotic objects like black hole binaries are expected to produce gravitational waves. Two of the pulsar experts leading this project are Scott Ransom from NRAO, whose enthusiasm for pulsars is well explained by the papers he writes, like this one: "Pulsars are cool. Seriously" and Victoria Kaspi, from McGill University, seen here speculating about some possible applications of pulsar research.
So far I've emphasized spectacular features of neutron stars and some famous results. These stories capture a lot of attention and do an excellent job at promoting astrophysics, but most research occurs in the gaps between catchy headlines and Nobel prizes. These gaps contain plenty of room for excellent research, much of it about understanding the nature of neutron stars, rather than testing fundamental physics with them.
Some of the most important open questions about neutron stars concern their size and structure. How large are they? What makes up their atmosphere? What is their core like?
One key advantage that neutron stars have over black holes is that their surface is visible to us, enabling much to be be learned about their atmospheres and interior structure. For example, in 2009, Wynn Ho from the University of Southampton and Craig Heinke from the University of Alberta, found evidence for a carbon atmosphere on the neutron star in the Cassiopeia A supernova remnant, using NASA's Chandra X-ray Observatory (note: I work at the Chandra X-ray Center in the Education and Public Outreach Group). This resolved a mystery about the nature of the neutron star, as the press release and Nature paper explain. An interesting side-note: the researchers calculate that the carbon atmosphere is only about 4 inches thick, as shown in the figure, because it has been compressed by a surface gravity that is 100 billion times stronger than on Earth. We're used to talking about massive scales and distances in astronomy, not small ones.
The properties of the carbon atmosphere on the neutron star in the Cassiopeia A supernova remnant are remarkable. It is only about four inches thick, has a density similar to diamond and a pressure more than ten times that found at the center of the Earth. As with the Earth's atmosphere, the extent of an atmosphere on a neutron star is proportional to the atmospheric temperature and inversely proportional to the surface gravity. The temperature is estimated to be almost two million degrees, much hotter than the Earth's atmosphere. However, the surface gravity on Cas A is 100 billion times stronger than on Earth, resulting in an incredibly thin atmosphere. Caption taken from Chandra web-site. Credit: NASA/CXC/M.Weiss
Heinke and Ho followed up this work with an even more interesting result, the first direct evidence for a superfluid, a bizarre, friction-free state of matter, at the center of a neutron star. First, a 4% drop in the temperature of the Cas A neutron star over 10 years was observed with Chandra and reported by Heinke et al. Then, two different papers, one in Physics Review Letters led by Dany Page from the National Autonomous University in Mexico and another in Monthly Notices of the Royal Astronomical Society led by Peter Shternin from the Ioffe Institute in St Petersburg, Russia independently came up with the same explanation. When the temperature of the neutron star fell below a critical level, a superfluid formed in the core of the star, forming neutrinos which travel outwards, taking energy with them. This causes the star to cool rapidly as observed with Chandra.
This image shows a composite of X-rays from Chandra (red, green, and blue) and optical data from the Hubble Space telescope (gold) of Cassiopeia A, the remains of a massive star that exploded in a supernova. The artist’s illustration in the inset shows a cutout of the interior of the neutron star where densities increase from the crust (orange) to the core (red) and finally to the part of the core where evidence for a superfluid has been found (inner red ball). The blue rays emanating from the center of the star represent the copious numbers of neutrinos -- nearly massless, weakly interacting particles -- that are created as the core temperature falls below a critical level and a neutron superfluid is formed, a process that began about 100 years ago as observed from Earth. These neutrinos escape from the star, taking energy with them and causing the star to cool much more rapidly. Credit: X-ray: NASA/CXC/UNAM/Ioffe/D.Page,P.Shternin et al; Optical: NASA/STScI; Illustration: NASA/CXC/M.Weiss
Other important information about the structure of neutron stars comes from studying the relationship between their size and mass. For a given mass, the size of a neutron star will depend on how stiff or soft the structure is. These are all relative terms, since by Earthly standards, nothing about neutron stars is soft.
Old neutron stars are typically faint objects, but when they pull material away from companion stars they can become much brighter, allowing good studies of their atmospheres. Observations of the amount of X-rays at different wavelengths, combined with theoretical models for their atmospheres, can allow the relationship between the radius and mass of the neutron star to be estimated. This work has been performed by Heinke, by Natalie Webb and Didier Barret (both from the Institut de Recherche en Astrophysique et Planétologie) as explained in this paper, and by Sebastien Guillot (Seb_Guillot on Twitter) from McGill University, in this paper. All of these observations were of neutron star binaries in globular clusters.
Neutron stars pulling material away from companions have also been observed to undergo bursts of X-rays, caused by thermonuclear explosions on their surfaces. These explosion can cause the atmosphere of the neutron star to expand. If observers catch one of these bursts they can follow as the star cools and calculate its surface area. When this area is combined with independent estimates of the distance to the neutron star, the relationship between the mass and radius of this object can be estimated. Two researchers who have applied this technique with great success are Feryal Ozel from the University of Arizona and Tolga Guver from Sabanci University, as described in this set of papers here, here, here, and here.
Each of the papers quoted in the previous two paragraphs provide information about the mass and radius of the neutron star and about their structure. However, there may be problems with relying too much on a single technique or a single object. A very good new paper by Andrew Steiner, from University of Washington, avoids this problem by combining all of the papers mentioned above: 4 neutron stars in globular clusters quietly pulling material from a companion and 4 undergoing X-ray bursts.
A Chandra X-ray Observatory image of 47 Tucanae, my favorite globular cluster. One of the neutron star binaries from Steiner et al. (2013), called X7, is labeled. Credit:NASA/CXC/Michigan State/A.Steiner et al.
Steiner et al. take these results and apply the latest neutron star models to estimate that the radius of a neutron star with a mass that is 1.4 times the mass of the Sun - a typical value - is between 10.4 and 12.9 km (6.5 to 8.0 miles), as we reported recently in a Chandra image release. They also estimate that the density at the center of a neutron star is almost ten times that of nuclear matter found in Earth-like conditions. This is equivalent to a pressure that is over ten trillion trillion times the pressure required for diamonds to form inside the Earth.
Using their results, Steiner et al. are able to compare their results with values derived from nuclear physics experiments performed on Earth, such as the distance between protons and neutrons in atomic nuclei. A larger neutron star radius implies that, on average, neutrons and protons in a heavy nucleus like Uranium are farther apart.
What is the core of a neutron star made of? It could be neutrons or it could be free quarks, the fundamental particles that combine to form protons and neutrons but which are not usually found in isolation. The paper by Steiner et al. cannot distinguish between these two possibilities, but there is potential to do so with future neutron star work.
There are many other interesting and important results about neutron stars. Regarding their structure, there are the very strong constraints that have come from pulsar work, such as the mass measurement of (1.97+/-0.04) solar masses by Demorest et al. (2010), with Scott Ransom as a co-author, that has already accumulated over 400 citations! An even larger neutron star mass might have been found by Romani et al. (2012). Then there are the astonishing spin rates that these incredibly massive, city-sized objects can reach, such as PSR J1748-2446ad which spins around 716 times a second, as reported by Hessels et al. (2006), with Ransom and Victoria Kaspi as co-authors.
I will continue to follow developments in neutron star research closely, as part of my job with Chandra but also because of my excellent location at Harvard-Smithsonian Center for Astrophysics (CfA), which has a regular stream of visitors covering a wide range of astrophysics. For example, Scott Ransom is giving a talk in early April about NANOGrav.
In the meantime, I may write a blog post or two on black holes, which are rumored to be interesting objects.
An interdisciplinary and international group from Chandra, the Smithsonian Astrophysical Observatory, and experts in the field of aesthetics from the University of Otago, New Zealand, formed the Aesthetics and Astronomy group - known as the A&A project -- back in 2008 to explore how astronomy images are perceived.
Amanda Berry, an MFA graduate student at Kendall College of Art and Design in Michigan, is researching "space" as a visual knowledge field. She asked some great questions to the Aesthetics & Astronomy project, which Jeffrey Smith kindly answered. We thought you might enjoy the read:
-------------------------------------------------------------------------------------------------------------------------------------------- Pushing the very boundaries of observation with new tools and innovation, technology allows us to see father and father into the unknown. Hauntingly beautiful, what can we learn from the images of the universe?
Technology does indeed allow us to see farther than we ever have before. And what we see is indeed stunning. But what do we learn? Well, one of the things we have discovered in our research is that it very much depends on who you are, and to a lesser degree, what kinds of information are provided to support that viewing. We have been using tools from the psychology of aesthetics to look at how regular people (like you and me) look at space images, and we have compared that to what astrophysicists see in them. You can read about this in some of our articles (which is probably how you found our group in the first place), but to summarize quickly, the general public starts with awe, and works their way toward trying to understand just what it is they are looking at. Astrophysicists kind of work the other way around. Those images are basically "data" to them. They interpret them the way a radiologist would look at an x-ray. What am I looking at? What was the purpose of producing the work in this fashion? What did the maker of the work want to highlight here? And if you ask an astrophysicist what is particularly interesting or important in a work he/she might point to something you didn't even notice was there!
Is space the next "terra incognita"? What drives us to search out and discover new things?
Well, I would turn to work in evolutionary psychology to answer that question (and that isn't my field!). But if you look at the history of humankind, you always see people reaching out, trying to find out what is around the next corner, over the next hill, beyond the horizon. Lisa and I live in New Zealand. About 1000 years ago, the Maori people left their island (not sure which one, but could have been Hawaii), in hand-built canoes, and took to the ocean to find new land. They travelled thousands of miles in these canoes to reach New Zealand. No certainty of food or fresh water, no idea what they might find or whom they might find there. And yet, they launched those canoes into the ocean. I think space is our frontier, but we explore it in different ways than other explorations.
The furthest reaches of our dreams, the most unimaginable, space lies at the foremost focus of scientists and dreamers, but is the quest for discovery dead?
I think that whenever we hit hard economic times like we are currently experiencing, there is a natural tendency to ask, "What is critical and what is just desirable?" I think we are seeing some of that. But, hard economic times abate, and I think the quest for discovery doesn't die, it just occasionally gets assigned a lesser priority. It's a bit hard to think that the last time we went to the moon was 40 years ago!
Phillip Fisher says in his book, Wonder, the Rainbow, and the Aesthetics of Rare Experiences “The experience of wonder no less than that of the sublime makes up part of the aesthetics of rare experiences. Each depends on moment in which we find ourselves struck by effects within nature whose power over us depends on their not being common or everyday.” Would images from space fall into this category of wonder and the sublime?
Well, let's start by defining sublime. Most folks think of the sublime as simply something that is the ultimate in wonderfulness; but that isn't what sublime means (and perhaps you already know this!). In art, the sublime is something that invokes a sense of awe and wonder that is tinged with fear or terror. There is typically the notion that there is danger lurking. You might see this in a painting where the perspective of the painter must be on a cliff edge or in front of a roaring oceanfront. If you go outside on a very clear moonless night and look at the sky, sometimes it seems overwhelming, and even a bit scary. That is the sublime. I think that space images fall into that category, especially if you seen them projecting very large as in an Imax or planetarium. If, on the other hand, you see them on your iPad, they are still wonderful and intriguing, but maybe slightly less inspiring of awe.
How does our being sighted creatures affect our quest for knowledge of the unknown? What are the limits of human vision and what role does technology play in the visual experience of space?
Very interesting question. Let me start simply. There is an ancient reptile that lives in New Zealand called the tuatara. When it is born, it has a very rudimentary third eye on the top of its head. It can only differentiate light and dark with this eye. The speculation is that this eye lets it spot danger from predator birds flying overhead. Human eyes have developed for human purposes, and looking at the stars really isn't all that important from an evolutionary perspective. That is, we do navigate from the stars, and determine when to plant crops from the location of constellations, etc., but it isn't really necessary to see the craters of the moon or the canals on Mars. Compare our eyes to that of a hawk that can see a mouse at a mile, or a possum that can see perfectly clearly at night. But all of that changed with the invention of the telescope, and then again with telescopes sent into space. We combine the data that we get from these telescopes with some creative assignation of colors and intensities to those data, and we find that there is much that we can make sense of and speculate on in space. And then we discover that not only are these images highly informative, they are stunningly beautiful as well.
How is the general public supposed to interpret the images of space? Is there a codex somewhere that would enlighten us as to what the colors mean?
Unfortunately, there is no codex (well maybe in a Dan Brown novel). And that is a big reason why we are conducting the research that we do. We are trying to find out what kinds of information and at what levels people respond to best.
