What Exactly Should We See When a Star Splashes into a Black Hole Event Horizon?

What Exactly Should We See When a Star Splashes into a Black Hole Event Horizon?:

At the center of our Milky Way galaxy dwells a behemoth. An object so massive that nothing can escape its gravitational pull, not even light. In fact, we think most galaxies have one of them. They are, of course, supermassive black holes.

Supermassive black holes are stars that have collapsed into a singularity. Einstein’s General Theory of Relativity predicted their existence. And these black holes are surrounded by what’s known as an event horizon, which is kind of like the point of no return for anything getting too close to the black hole. But nobody has actually proven the existence of the event horizon yet.

Some theorists think that something else might lie at the center of galaxies, a supermassive object event stranger than a supermassive black hole. Theorists think these objects have somehow avoided a black hole’s fate, and have not collapsed into a singularity. They would have no event horizon, and would have a solid surface instead.

“Our whole point here is to turn this idea of an event horizon into an experimental science, and find out if event horizons really do exist or not,” – Pawan Kumar Professor of Astrophysics, University of Texas at Austin.

A team of researchers at the University of Texas at Austin and Harvard University have tackled the problem. Wenbin Lu, Pawan Kumar, and Ramesh Narayan wanted to shed some light onto the event horizon problem. They wondered about the solid surface object, and what would happen when an object like a star collided with it. They published their results in the Monthly Notices of the Royal Astronomical Society.

Artist’s conception of the event horizon of a black hole. Credit: Victor de Schwanberg/Science Photo Library

“Our whole point here is to turn this idea of an event horizon into an experimental science, and find out if event horizons really do exist or not,” said Pawan Kumar, Professor of Astrophysics at The University of Texas at Austin, in a press release.

Since a black hole is a star collapsed into a singularity, it has no surface area, and instead has an event horizon. But if the other theory turns out to be true, and the object has a solid surface instead of an event horizon, then any object colliding with it would be destroyed. If a star was to collide with this hard surface and be destroyed, the team surmised, then the gas from the star would enshroud the object and shine brightly for months, or even years.

This is the first in a sequence of two artist’s impressions that shows a huge, massive sphere in the center of a galaxy, rather than a supermassive black hole. Here a star moves towards and then smashes into the hard surface of the sphere, flinging out debris. The impact heats up the site of the collision. Image:
Mark A. Garlick/CfA

In this second artist’s impression a huge sphere in the center of a galaxy is shown after a star has collided with it. Enormous amounts of heat and a dramatic increase in the brightness of the sphere are generated by this event. The lack of observation of such flares from the center of galaxies means that this hypothetical scenario is almost completely ruled out. Image: Mark A. Garlick/CfA

If that were the case, then the team knew what to look for. They also worked out how often this would happen.

“We estimated the rate of stars falling onto supermassive black holes,” Lu said in the same press release. “Nearly every galaxy has one. We only considered the most massive ones, which weigh about 100 million solar masses or more. There are about a million of them within a few billion light-years of Earth.”

Now they needed a way to search the sky for these objects, and they found it in the archives of the Pan-STARRS telescope. Pan-STARRS is a 1.8 meter telescope in Hawaii. That telescope recently completed a survey of half of the northern hemisphere of the sky. In that survey, Pan-STAARS spent 3.5 years looking for transient objects in the sky, objects that brighten and then fade. They searched the Pan-STARR archives for transient objects that had the signature they predicted from stars colliding with these supermassive, hard-surfaced objects.



The trio predicted that in the 3.5 year time-frame captured by the Pan-STAARS survey, 10 of these collisions would occur and should be represented in the data.

“It turns out it should have detected more than 10 of them, if the hard-surface theory is true.” – Wenbin Lu, Dept. of Astronomy, University of Texas at Austin.

“Given the rate of stars falling onto black holes and the number density of black holes in the nearby universe, we calculated how many such transients Pan-STARRS should have detected over a period of operation of 3.5 years. It turns out it should have detected more than 10 of them, if the hard-surface theory is true,” Lu said.

The team found none of the flare-ups they expected to see if the hard-surface theory is true.

“Our work implies that some, and perhaps all, black holes have event horizons…” – Ramesh Narayan, Harvard-Smithsonian Center for Astrophysics.

What might seem like a failure, isn’t one of course. Not for Einstein, anyway. This represents yet another successful test of Einstein’s Theory of General Relativity, showing that the event horizon predicted in his theory does seem to exist.

As for the team, they haven’t abandoned the idea yet. In fact, according to Pawan Kumar, Professor of Astrophysics, University of Texas at Austin, “Our motive is not so much to establish that there is a hard surface, but to push the boundary of knowledge and find concrete evidence that really, there is an event horizon around black holes.”

“General Relativity has passed another critical test.” – Ramesh Narayan, Harvard-Smithsonian Center for Astrophysics.

“Our work implies that some, and perhaps all, black holes have event horizons and that material really does disappear from the observable universe when pulled into these exotic objects, as we’ve expected for decades,” Narayan said. “General Relativity has passed another critical test.”

The team plans to continue to look for the flare-ups associated with the hard-surface theory. Their look into the Pan-STARRS data was just their first crack at it.

An artist’s illustration of the Large Synoptic Survey Telescope with a simulated night sky. The team hopes to use the LSST to further refine their search for hard-surface supermassive objects. Image: Todd Mason, Mason Productions Inc. / LSST Corporation

They’re hoping to improve their test with the upcoming Large Synoptic Survey Telescope (LSST) being built in Chile. The LSST is a wide field telescope that will capture images of the night sky every 20 seconds over a ten-year span. Every few nights, the LSST will give us an image of the entire available night sky. This will make the study of transient objects much easier and effective.

More reading: Rise of the Super Telescopes: The Large Synoptic Survey Telescope

Sources:

• Do Stars Fall Quietly into Black Holes, or Crash into Something Utterly Unknown?
• Stellar disruption events support the existence of the black hole event horizon

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Flying Into the Sun? NASA’s Parker Solar Probe Mission

Flying Into the Sun? NASA’s Parker Solar Probe Mission:



If you’ve read enough of our articles, you know I’ve got an uneasy alliance with the Sun. Sure, it provides the energy we need for all life on Earth. But, it’s a great big ongoing thermonuclear reaction, and it’s right there! As soon as we get fusion, Sun, in like, 30 years or so, I tell you, we’ll be the ones laughing.

But to be honest, we still have so many questions about the Sun. For starters, we don’t fully understand the solar wind blasting out of the Sun. This constant wind of charged particles is constantly blowing out into space, but sometimes it’s stronger, and sometimes it’s weaker.

What are the factors that contribute to the solar wind? And as you know, these charged particles are not healthy for the human body, or for our precious electronics. In fact, the Sun occasionally releases enormous blasts that can damage our satellites and electrical grids.

How can we predict the intensity so that we can be better prepared for dangerous solar storms? Especially the Carrington-class events that might take down huge portions of our modern society.

Perhaps the biggest mystery with the Sun is the temperature of its corona. The surface of the Sun is hot, like 5,500 degrees Celsius. But if you rise up into the atmosphere of the Sun, into its corona, the temperature jumps beyond a million degrees.

The list of mysteries is long. And to start understanding what’s going on, we’ll need to get much much closer to the Sun.

Good news, NASA has a new mission in the works to do just that.

The Parker Solar Probe logo. Credit: NASA/JHUAPL

The mission is called the Parker Solar Probe. Actually, last week, it was called the Solar Probe Plus, but then NASA renamed it, and that reminded me to do a video on it.

It’s pretty normal for NASA to rename their spacecraft, usually after a dead astronomer/space scientist, like Kepler, Chandra, etc. This time, though, they renamed it for a legendary solar astronomer Eugene Parker, who developed much of our modern thinking on the Sun’s solar wind. Parker just turned 90 and this is the first time NASA has named it after someone living.

Anyway, back to the spacecraft.

The mission is due to launch in early August 2018 on a Delta IV Heavy, so we’re still more than a year away at this point. When it does, it’ll carry the spacecraft on a very unusual trajectory through the inner Solar System.

The problem is that the Sun is actually a very difficult place to reach. In fact, it’s the hardest place to get to in the entire Solar System.

Remember that the Earth is traveling around the Sun at a velocity of 30 km/s. That’s almost three times the velocity it takes to get into orbit. That’s a lot of velocity.

In order to be able to get anywhere near the Sun, the probe needs to shed velocity. And in order to do this, it’s going to use gravitational slingshots with Venus. We’ve talked about gravitational slingshots in the past, and how you can use them to speed up a spacecraft, but you can actually do the reverse.

The Parker Solar Probe will fall down into Venus’ gravity well, and give orbital velocity to Venus. This will put it on a new trajectory which takes it closer to the Sun. It’ll do a total of 7 flybys in 7 years, each of which will tweak its trajectory and shed some of that orbital momentum.

Parker Solar Probe’s trajectory including Venus flybys. Credit: NASA/JHUAPL

You know, trying to explain orbital maneuvering is tough. I highly recommend that you try out Kerbal Space Program. I’ve learned more about orbital mechanics by playing that game for a few months than I have in almost 2 decades of space journalism. Go ahead, try to get to the Sun, I challenge you.

Anyway, with each Venus flyby, the Parker Solar Probe will get closer and closer to the Sun, well within the orbit of Mercury. Far closer than any spacecraft has ever gotten to the Sun. At its closest point, it’ll only be 5.9 million kilometers from the Sun. Just for comparison, the Earth orbits at an average distance of about 150 million kilometers. That’s close.

And over the course of its entire mission, the spacecraft is expected to make a total of 24 complete orbits of the Sun, analyzing that plasma ball from every angle.

The orbit is also highly elliptical, which means that it’s going really really fast at its closest point. Almost 725,000 km/h.

In order to withstand the intense temperatures of being this close to the Sun, NASA has engineered the Parker Solar Probe to shed heat. It’s equipped with an 11.5 cm-thick shield made of carbon-composite. For that short time it spends really close to the Sun, the spacecraft will keep the shield up, blocking that heat from reaching the rest of its instruments.

And it’s going to get hot. We’re talking about more than 1,300 degrees Celsius, which is about 475 times as much energy as a spacecraft receives here on Earth. In the outer Solar System, the problem is that there just isn’t enough energy to power solar panels. But where Parker is going, there’s just too much energy.

Now we’ve talked about the engineering difficulties of getting a spacecraft this close to the Sun, let’s talk about the science.

Coronal holes are regions in the sun’s atmosphere or corona where solar plasma can stream directly into space. Often a hole will a couple rotations, inciting repeat auroras approximately every 4 weeks. Credit: NASA

The biggest question astronomers are looking to solve is, how does the corona get so hot. The surface is 5,500 Celsius. As you get farther away from the Sun, you’d expect the temperature to go down. And it certainly does once you get as far as the orbit of the Earth.

But the Sun’s corona, or its outer atmosphere, extends millions of kilometers into space. You can see it during a solar eclipse as this faint glow around the Sun. Instead of dropping, the temperature rises to more than a million degrees.

What could be causing this? There are a couple of ideas. Plasma waves pushed off the Sun could bunch up and release their heat into the corona. You could also get the crisscrossing of magnetic field lines that create mini-flares within the corona, heating it up.

The second great mystery is the solar wind, the stream of charged protons and electrons coming from the Sun. Instead of a constant blowing wind, it can go faster or slower. And when the speed changes, the contents of the wind change too.

There’s the slow wind, that goes a mere 1.1 million km/h and seems to emanate from the Sun’s equatorial regions. And then the fast wind, which seems to be coming out of coronal holes, cooler parts in the Sun’s corona, and can be going at 2.7 million km/h.

Why does the solar wind speed change? Why does its consistency change?

Parker Solar Probe’s instruments. Credit: NASA/JHUAPL

The Parker Solar Probe is equipped with four major instruments, each of which will gather data from the Sun and its environment.

The FIELDS experiment will measure the electric and magnetic fields and waves around the Sun. We know that much of the Sun’s behavior is driven by the complex interaction between charged plasma in the Sun. In fact, many physicists agree that magnetohydrodynamics is easily one of the most complicated fields you can get into.

Integrated Science Investigation of the Sun, or ISOIS (which I suspect needs a renaming) will measure the charged particles streaming off the Sun, during regular solar activity and during dangerous solar storms. Can we get any warning before these events occur, giving astronauts more time to protect themselves?

Wide-field Imager for Solar PRobe or WISPR is its telescope and camera. It’s going to be taking close up, high resolution images of the Sun and its corona that will blow our collective minds… I hope. I mean, if it’s just a bunch of interesting data and no pretty pictures, it’s going to be hard to make cool videos showcasing the results of the mission. You hear me NASA, we want pictures and videos. And science, sure.

And then the Solar Wind Electrons Alphas and Protons Investigation, or SWEAP, will measure type, velocity, temperature and density of particles around the Sun, to help us understand the environment around it.

One interesting side note, the spacecraft will be carrying a tiny chip on board with photos of Eugene Parker and a copy of his original 1958 paper explaining the Sun’s solar wind.

The Parker Solar Probe orbiting the Sun. Credit: NASA/JHUAPL

I know we’re still more than a year away from liftoff, and several years away before the science data starts pouring in. But you’ll be hearing more and more about this mission shortly, and I’m pretty excited about what it’s going to accomplish. So stay tuned, and once the science comes in, I’m sure you’ll hear plenty more about it.

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The Sun Probably Lost a Binary Twin Billions of Years Ago

The Sun Probably Lost a Binary Twin Billions of Years Ago:

For us Earthlings, life under a single Sun is just the way it is. But with the development of modern astronomy, we’ve become aware of the fact that the Universe is filled with binary and even triple star systems. Hence, if life does exist on planets beyond our Solar System, much of it could be accustomed to growing up under two or even three suns. For centuries, astronomers have wondered why this difference exists and how star systems came to be.

Whereas some astronomers argue that individual stars formed and acquired companions over time, others have suggested that systems began with multiple stars and lost their companions over time. According to a new study by a team from UC Berkeley and the Harvard-Smithsonian Center for Astrophysics (CfA), it appears that the Solar System (and other Sun-like stars) may have started out as binary system billions of years ago.

This study, titled “Embedded Binaries and Their Dense Cores“, was recently accepted for publication in the Monthly Notices of the Royal Astronomical Society. In it, Sarah I. Sadavoy – a radio astronomer from the Max Planck Institute for Astronomy and the CfA – and Steven W. Stahler (a theoretical physicist from UC Berkeley) explain how a radio surveys of a star nursery led them to conclude that most Sun-like stars began as binaries.

The dark molecular cloud, Barnard 68, is a stellar nursery that can only be studied using radio astronomy. Credit: FORS Team, 8.2-meter VLT Antu, ESO

They began by examining the results of the first radio survey of the giant molecular cloud located about 600 light-years from Earth in the Perseus constellation – aka. the Perseus Molecular Cloud. This survey, known as the VLA/ALMA Nascent Disk and Multiplicity (VANDAM) survey, relied the Very Large Array in New Mexico and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to conduct the first survey of the young stars (<4 million years old) in this star-forming region.

For several decades, astronomers have known that stars are born inside “stellar nurseries”, which are the dense cores that exist within immense clouds of dust and cold, molecular hydrogen. These clouds look like holes in the star field when viewed through an optical telescope, thanks to all the dust grains that obscure light coming from the stars forming within them and from background stars.

Radio surveys are the only way to probe these star-forming regions, since the dust grains emit radio transmissions and also do not block them. For years, Stahler has been attempting to get radio astronomers to examine molecular clouds in the hope of gathering information on the formation of young stars inside them. To this end, he approached Sarah Sadavoy – a member of the VANDAM team – and proposed a collaboration.

The two began their work together by conducting new observations of both single and binary stars within the dense core regions of the Perseus cloud. As Sadavoy explained in a Berkeley News press release, the duo were looking for clues as to whether young stars formed as individuals or in pairs:

“The idea that many stars form with a companion has been suggested before, but the question is: how many? Based on our simple model, we say that nearly all stars form with a companion. The Perseus cloud is generally considered a typical low-mass star-forming region, but our model needs to be checked in other clouds.”

Infrared image from the Hubble Space Telescope, showing a bright, fan-shaped object (lower right quadrant) thought to be a binary star that emits light pulses as the two stars interact. Credit: NASA/ESA/ J. Muzerolle (STScI)

Their observations of the Perseus cloud revealed a series of Class 0 and Class I stars – those that are <500,000 old and 500,000 to 1 million years old, respectively – that were surrounded by egg-shaped cocoons. These observations were then combined with the results from VANDAM and other surveys of star forming regions – including the Gould Belt Survey and data gathered by SCUBA-2 instrument on the James Clerk Maxwell Telescope in Hawaii.

From this, they created a census of stars within the Perseus cloud, which included 55 young stars in 24 multiple-star systems (all but five of them binary) and 45 single-star systems. What they observed was that all of the widely separated binary systems – separated by more than 500 AU – were very young systems containing two Class 0 stars  that tended to be aligned with the long axis of their egg-shaped dense cores.

Meanwhile, the slightly older Class I binary stars were closer together (separated by about 200 AU) and did not have the same tendency as far as their alignment was concerned. From this, the study’s authors began mathematically modelling multiple scenarios to explain this distribution, and concluded that all stars with masses comparable to our Sun start off as wide Class 0 binaries. They further concluded that 60% of these split up over time while the rest shrink to form tight binaries.

“As the egg contracts, the densest part of the egg will be toward the middle, and that forms two concentrations of density along the middle axis,” said Stahler. “These centers of higher density at some point collapse in on themselves because of their self-gravity to form Class 0 stars. “Within our picture, single low-mass, sunlike stars are not primordial. They are the result of the breakup of binaries. ”

The two brightest stars of the Centaurus constellation, the binary star system of Alpha Centauri. Credit: Wikipedia Commons/Skatebiker

Findings of this nature have never before been seen or tested. They also imply that each dense core within a stellar nursery (i.e. the egg-shaped cocoons, which typically comprise a few solar masses) converts twice as much material into stars as was previously thought. As Stahler remarked:

“The key here is that no one looked before in a systematic way at the relation of real young stars to the clouds that spawn them. Our work is a step forward in understanding both how binaries form and also the role that binaries play in early stellar evolution. We now believe that most stars, which are quite similar to our own sun, form as binaries. I think we have the strongest evidence to date for such an assertion.”

This new data could also be the start of a new trend, where astronomers rely on radio telescopes to examine dense star-forming regions with the hopes of witnessing more in the way of stellar formations. With the recent upgrades to the VLA and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, and the ongoing data provided by the SCUBA-2 survey in Hawaii, these studies may be coming sooner other than later.

Another interesting implication of the study has to do with something known as the “Nemesis hypothesis”. In the past, astronomers have conjectured that a companion star named “Nemesis” existed within our Solar System. This star was so-named because the theory held that it was responsible for kicking the asteroid which caused the extinction of the dinosaurs into Earth’s orbit. Alas, all attempts to find Nemesis ended in failure.

Artist’s impression of the binary star system of Sirius, a white dwarf star in orbit around Sirius (a white supergiant). Credit: NASA, ESA and G. Bacon (STScI)

As Steven Stahler indicated, these findings could be interpreted as a new take on the Nemesis theory:

“We are saying, yes, there probably was a Nemesis, a long time ago. We ran a series of statistical models to see if we could account for the relative populations of young single stars and binaries of all separations in the Perseus molecular cloud, and the only model that could reproduce the data was one in which all stars form initially as wide binaries. These systems then either shrink or break apart within a million years.”

So while their results do not point towards a star being around for the extinction of the dinosaurs, it is possible (and even highly plausible) that billions of years ago, the Solar planets orbited around two stars. One can only imagine what implications this could have for the early history of the Solar System and how it might have affected planetary formation. But that will be the subject of future studies, no doubt!

Further Reading: Berkeley News, arXiv

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LISA is On! Gravitational Wave Detection is Going to Space

LISA is On! Gravitational Wave Detection is Going to Space:

The discovery of gravitational waves by the LIGO experiment in 2015 sent ripples through the scientific community. Originally predicted by Einstein’s Theory of General Relativity, the confirmation of these waves (and two subsequent detections) solved a long-standing cosmological mystery. In addition to bending the fabric of space-time, it is now known that gravity can also create perturbations that can be detected billions of light-years away.

Seeking to capitalize on these discoveries and conduct new and exciting research into gravitational waves, the European Space Agency (ESA) recently green-lighted the Laser Interferometer Space Antenna (LISA) mission. Consisting of three satellites that will measure gravitational waves directly through laser interferometry, this mission will be the first space-based gravitational wave detector.

This decision was announced yesterday (Tuesday, June 20th) during a meeting of ESA’s Science Program Committee (SPC). It’s implementation is part of the ESA’s Cosmic Vision plan – the current cycle of the agency’s long-term planning for space science missions – which began in 2015 and will be running until 2025. It is also in keeping with the ESA’s desire to study the “invisible universe“, a policy that was adopted in 2013. 

http://sci.esa.int/science-e-media/video/63/367_ESA_LISA_Pathfinder_journey_to_L1_20151019_512p.mp4

To accomplish this, the three satellites that make up the LISA constellation will be deployed into orbit around Earth. Once there, they will assume a triangular formation – spaced 2.5 million km (1.55 million mi) apart – and follow Earth’s orbit around the Sun. Here, isolated from all external influences but Earth’s gravity, they will then connect to each other by laser and begin looking for minute perturbations in the fabric of space-time.

Much like how the LIGO experiment and other gravitational wave detectors work, the LISA mission will rely on laser interferometry. This process consists of a beam of electromagnetic energy (in this case, a laser) being split in two and then recombined to look for patterns of interference. In LISA’s case, two satellites play the role of reflectors while the remaining one is the both source of the lasers and the observer of the laser beam.

When a gravitational wave passes through the triangle established by the three satellites, the lengths of the two laser beams will vary due to the space-time distortions caused by the wave. By comparing the laser beam frequency in the return beam to the frequency of the sent beam, LISA will be able to measure the level of distortion.

These measurements will have to be extremely precise, since the distortions they are looking for affect the fabric of space-time on the most minuscule of levels – a few millionths of a millionth of a meter over a distance of a million kilometers. Luckily, the technology to detect these waves has already been tested by the LISA Pathfinder mission, which deployed in 2015 and will conclude its mission at the end of the month.

Artist’s concept of the LISA mission. Credit: AEI/Milde Marketing/Exozet

In the coming weeks and months, the ESA will be looking over the design of the LISA mission and completing a cost assessment. If all goes as planned, the mission will be proposed for “adoption” before construction begins and it is expected to be launched by 2034. In the same meeting, the ESA also adopted another important mission that will be searching for exoplanets in the coming years.

This mission is known as the PLAnetary Transits and Oscillations of stars, or PLATO, mission. Like Kepler, this mission will monitor stars within a large sections of the sky to look for small dips in their brightness, which are caused by planets passing between the star and the observer (i.e. the transit method). Originally selected in February of 2014, this mission is now moving from the blueprint phase into construction and will launch in 2026.

It’s an exciting time for the European Space Agency. In recent years, it has committed itself to multiple endeavors in the hope of maintaining Europe’s commitment to and continued presence in space. These include studying the “invisible universe”, mounting missions to the Moon and Mars, maintaining a commitment to the International Space Station, and even building a successor to the ISS on the Moon!

https://upload.wikimedia.org/wikipedia/commons/transcoded/a/a4/BBH_gravitational_lensing_of_gw150914.webm/BBH_gravitational_lensing_of_gw150914.webm.480p.webm

Further Reading: ESA

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Let’s Clean up the Space Junk with Magnetic Space Tugs

Let’s Clean up the Space Junk with Magnetic Space Tugs:

After 50 years of sending rockets, satellites, and payloads into orbit, humanity has created something of a “space junk” problem. Recent estimates indicate that there are more than 170 million pieces of debris up there, ranging in size from less than 1 cm (o.4 in) to a few meters in diameter. Not only does this junk threaten spacecraft and the ISS, but collisions between bits of debris can cause more to form, a phenomena known as the Kessler Effect.

And thanks to the growth of the commercial aerospace industry and the development of small satellites, things are not likely to get any less cluttered up there anytime soon. Hence why multiple strategies are being explored to clean up the space lanes, ranging from robotic arms and nets to harpoons. But in what may be the most ambitious plan to date, the ESA has proposed creating space tugs with powerful magnets to yank debris out of orbit.

The concept comes from Emilien Fabacher, a researcher from the Institut Supérieur de l’Aéronautique et de l’Espace at the University of Toulouse, France. His concept for a magnetic tug seeks to address one type of space debris in particular – inoperable satellites. These uncontrolled, rapidly spinning objects often weigh up to several tons, and are therefore one of the most significant collision hazards there is.

Illustration showing the problem of space debris. Credit: ESA

When applied to the problem of orbital debris, magnetic attraction is an attractive solutions for the safe deorbiting of spent satellites. For starters, it relies on technology that is standard issue aboard many low-orbiting satellites, which is known as magnetorquers. These electromagnets allow satellites to adjust their orientation using the Earth’s magnetic field. Hence, debris-chasing satellites would not need to be specially equipped in advance.

What’s more, this same magnetic attraction or repulsion technology is being considered as a safe method for allowing multiple satellites to maintain close formations in space. Such satellites – like NASA’s Magnetospheric Multiscale mission (MMS), the Landsat 7 and the Earth Observing-1 satellites, and the ESA’s upcoming LISA mission – are either operational or soon will be around Earth.

Because of this, this kind of magnetic attraction technology presents a safe and effective alternative for deorbiting space junk. As Fabacher explained in a recent ESA press release:

“With a satellite you want to deorbit, it’s much better if you can stay at a safe distance, without needing to come into direct contact and risking damage to both chaser and target satellites. So the idea I’m investigating is to apply magnetic forces either to attract or repel the target satellite, to shift its orbit or deorbit it entirely.”

Artist’s impression of the ESA’s proposed Darwin mission, six formation-flying satellites that would look for exoplanets. Credit: ESA/Medialab

The concept emerged out of a conversation Fabacher had with experts from the ESA’s technical center in the Netherlands. As part of his PhD research, he was looking into how magnetic guidance, navigation and control techniques would work in practice. This led to a discussion about how similar technology could allow swarms of satellites to attract and remove debris from orbit.

After making some calculations that combined a rendezvous simulator with magnetic interaction models, and also taking account the ever-changing state of Earth’s own magnetosphere, Fabacher and his colleagues realized they had a working concept. “The first surprise was that it was indeed possible, theoretically – initially we couldn’t be sure, but it turns out that the physics works fine,” he said.

To break it down, the chaser satellites would generate a strong magnetic field using superconducting wires that are cooled to cryogenic temperatures. These satellites would also rely on magnetic fields to maintain precise flying formations, thus allowing a swarm of chaser satellites the ability to deal with multiple pieces of debris, or to coordinate and guide debris to a specific location.

According to Finn Ankersen – an ESA expert in rendezvous and docking and formation flight – these magnetic tugs would also be able to remove space debris with a very high level of precision. “This kind of contactless magnetic influence would work from about 10–15 meters out, offering positioning precision within 10 cm with attitude precision [of] 1 – 2º,” he said.

Why Space Debris Mitigation is needed. Click for animation. Credit: ESA

The concept is being developed with support provided by the ESA’s Networking/Partnering Initiative, a program that offers support to universities and research institutes for the sake of developing space-related technologies. And it comes at a time when the issue of space debris is becoming increasingly worrisome.

Left unchecked, space debris is likely to become a very serious hazard in the coming years and decades. Already, it is estimated that the small satellite market will grow by $5.3 billion in the next decade (according to Space Works and Eurostat) and many private companies are looking to provide regular launch services to accommodate that growth.

If we intend to begin making a return to the Moon and mounting missions to Mars, we need to make sure the space lanes are clear! And given the importance of the International Space Station to scientific research and international collaboration, and with companies like Bigelow Aerospace looking to establish space habitats in orbit, something has to be done about this problem before it gets completely out of control!

Who knows? Maybe a small fleet or magnetic tugs is just what we need to clean up this mess!

Further Reading: ESA

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Saturn Rides Bareback On The Galactic Dark Horse

Saturn Rides Bareback On The Galactic Dark Horse:

The bright dot is Saturn and it shines on the back of the Galactic Dark Horse, a collection of dark nebulae in the constellation Ophiuchus that resembles a prancing horse. The head is to the right with a wisp of a tail to the left. The photo, taken on June 20, 2017, has been turned 90° to the right, so the horse stands upright. Credit: Bob King

I didn’t notice it with the naked eye, but as soon as the time exposure ended and I looked at the camera’s back display, there it was — Saturn riding barebacked on the Galactic Dark Horse! The horse, more of a prancing pony, is a collection of dark nebulae in the southern sky beautifully placed for viewing on late June evenings. The Dark Horse is part of the Great Rift, a dark gap that splits the band of the Milky Way in half, starting at the Northern Cross and extending all the way down to the “Teapot” of Sagittarius in the south.

The Great Rift appears to unzip the summer Milky Way right down the middle. Saturn and the Dark Horse are seen at lower right. Credit: Bob King

While appearing to be little more than empty, starless space, in reality the Rift consists of enormous clouds of cosmic dust and gas in the plane of the galaxy called dark nebulae that blot out the light of more distant stars. If you could suck it all up with a monster vacuum cleaner and expose the billions of stars otherwise hidden, the Milky Way would cast obvious shadows — even suburban skywatchers would routinely see it.

Saturn dominates the scene at left center in this photo taken on June 20. To its right you can see the prancing pony standing on its tail with legs sticking out to the right. Several bright Milky Way star clouds are also visible including the Small Sagittarius Star Cloud (left) and the Large Sagittarius Star Cloud below and left of Saturn. Antares in Scorpius is at upper right. Can you find the firefly that flashed during the exposure? Credit: Bob King

Tiny dust particles spewed by older, evolved stars and exploding supernovas have been settling in the plane of the galaxy since its birth 13.2 billion years ago. While the dust is sparse, it adds up over the light years to form a thick, dark band silhouetted against the more distant stars. Gravity has been at work on the dust since the earliest days, compressing the denser clumps into new stars and star clusters. But much raw material remains. Within the curdles of dark nebulae, astronomers use dust-penetrating infrared and radio telescopes to watch new stars in the process of incubation.

Dense cores of dust within the Pipe Nebula are collapsing to form new stars. We can’t see them yet because of obscuring dust. The left end of the Pipe forms the long back leg and rump of the Dark Horse. The much smaller Snake Nebula (shaped like the letter “S”) is visible at top center. Credit and copyright: Yuri Beletsky

There are more obvious parts of the Rift to the naked eye but few conjure up as striking an image as the Dark Horse, located about one outstretched fist to the left of the Scorpius’ brightest star, Antares. Saturn sits astride the horse’s back or eastern side. While it’s fun to see the horse as a single figure, astronomers catalog the various body parts as individual dark nebulae with separate numbers and even names. The largest part of the horse, the hind leg, is nicknamed the Pipe Nebula and lies 600-700 light years away. The Pipe is further subdivided into B59, B72, B77 and B78, from a survey of dark nebulae by early 20th century American astronomer E.E. Barnard.

You’ll need dark skies and averted vision to spot the Dark Horse. Let Saturn and Antares be your guides. The nebula is highest in the sky around 12:30 a.m. in late June as shown in the map above. Latitude shown is 40° North. Created with Stellarium

While the dark horse shows up well in time-exposure photos, you’ll need dark, rural skies to view it with the naked eye. It’s only a couple fists high for those of us living in the northern U.S. and southern Canada, but considerably higher up from the southern states and points south. The figure is large but faint, about 10° long by 7° wide, and stands due south and highest in the sky around 12:30 a.m. in late June. Allow your eyes time to fully dark adapt beforehand. Try for the dark rump and hind leg first then work from there to fill in the rest of the horse.

If we could see the Milky Way galaxy edge-on from afar, it would look similar to NGC 891 in Andromeda. Both have long bands of interstellar dust along their equators that appear dark against the bright, starry backdrop. Credit: Hunter Wilson

Once I knew what to look for, I could fleetingly see the entire horse with its various protrusions as a subtle darkness against the brighter Milky Way. Averted vision, the technique of playing your eye around the subject rather than staring directly at it, helped make it happen. Wide-field binoculars will show it easily and in greater detail against a fabulously rich star field.

The best time to horse around under the Milky Way happens from now till the end of the month, when the bright Moon sends the critter into hiding.

The post Saturn Rides Bareback On The Galactic Dark Horse appeared first on Universe Today.

What Caused the Kuiper Belt to Get Warped?

What Caused the Kuiper Belt to Get Warped?:

Astronomers have known about the Kuiper Belt for decades, and were postulating about its existence long before it was even observed. Since that time, many discoveries have been made in this region of space – ranging from numerous minor planets to the fact that the orbital planes of Kuiper Belt Objects (KBOs) are widely dispersed – that have led to new theoretical models of the formation and evolution of the Solar System.

For instance, while conducting measurements of the mean plane of minor planets and KBOs, a team from the Lunar and Planetary Laboratory (LPL) at The University of Arizona discovered a warp in orbits of certain, highly-distant KBOs.  According to their study, this warp could be an indication of a planetary-mass object in the area, one which orbits our Sun even closer than the theoretical “Planet 9“.

The study – “The Curiously Warped Mean Plane of the Kuiper Belt” which is scheduled to be published in the Astronomical Journal – was produced by Kathryn Volk and Renu Malhotra (two astronomers with the LPL). As they stated in their study, the presence of this planet was confirmed by examining the orbits of icy bodies in the very outer reaches of the Solar System.

Artist’s impression of the yet-to-be-discovered “planetary mass object”, who’s existence has been theorized based on the orbital plane of distant Kuiper Belt objects. Credit: Heather Roper/LPL

Whereas most KBOs – which are leftover material from the formation of the Solar System – orbit the Sun close to the mean plane of the Solar System itself, the most distant objects do not. To determine why, the researchers analyzed the tilt angles of the orbital planes of more than 600 KBOs to determine the direction of their precession – i.e. the direction in which these rotating objects experience a change in their orientation.

As Malhotra – a Louise Foucar Marshall Science Research Professor and Regents’ Professor of Planetary Sciences at LPL – illustrated, KBOs operate in a way that is analogous to spinning tops:

“Imagine you have lots and lots of fast-spinning tops, and you give each one a slight nudge. If you then take a snapshot of them, you will find that their spin axes will be at different orientations, but on average, they will be pointing to the local gravitational field of Earth… We expect each of the KBOs’ orbital tilt angle to be at a different orientation, but on average, they will be pointing perpendicular to the plane determined by the Sun and the big planets.”

What they found was that the average plane of these objects was tilted away from the solar plane by about eight degrees, which suggests that a powerful gravitational force in the outer Solar System is tugging on them. “The most likely explanation for our results is that there is some unseen mass,” said Volk in UA News press release. “According to our calculations, something as massive as Mars would be needed to cause the warp that we measured.”

Animated diagram showing the spacing of the Solar Systems planet’s, the unusually closely spaced orbits of six of the most distant KBOs, and the possible “Planet 9”. Credit: Caltech/nagualdesign

According to their calculations, this Mars-size body would likely orbit the Sun at a distance of roughly 60 AU, and with an orbital inclination that was tilted eight degrees to the average plane of the known planets (i.e. the same tilt as the “warped” KBOs). Within these parameters, a planet of this size would have sufficient gravitational influence to warp the orbital plane of the distant KBOs to within 10 AU on either side of it.

In other words, a Mars-sized planet in the outer Kuiper Belt would be able to influence the orbital inclination of KBOs that are between 50 and 70 AUs from the Sun. This is certainly consistent with what we know about the Kuiper Belt, who’s orbital inclination appears to be consistently flat (i.e. consistent with the rest of the Solar System) past a distance of about 50 AU – but changes between a distance of 50 and 80 AU.

As Volk indicated, there is a possibility that this warping could be the result of a statistical fluke. But in the end, their calculations indicated that this is highly unlikely, and that the behavior of distant KBOs is consistent with the existence of a as-yet-unseen gravitational influence:

“But going further out from 50 to 80 AU, we found that the average plane actually warps away from the invariable plane. There is a range of uncertainties for the measured warp, but there is not more than 1 or 2 percent chance that this warp is merely a statistical fluke of the limited observational sample of KBOs… The observed distant KBOs are concentrated in a ring about 30 AU wide and would feel the gravity of such a planetary mass object over time, so hypothesizing one planetary mass to cause the observed warp is not unreasonable across that distance.”  

Artist’s impression of Planet Nine, blocking out the Milky Way. The Sun is in the distance, with the orbit of Neptune shown as a ring. Credit: ESO/Tomruen/nagualdesign

Another possibility is that another object entirely could have disturbed the plane of the outer Kuiper Belt – for instance, a star passing through the outer Solar System. But as Malhotra explained, this explanation is also a highly unlikely, as any disturbance caused by a passing star would only be temporary and would have manifested itself differently.

“A passing star would draw all the ‘spinning tops’ in one direction,” he said. “Once the star is gone, all the KBOs will go back to precessing around their previous plane. That would have required an extremely close passage at about 100 AU, and the warp would be erased within 10 million years, so we don’t consider this a likely scenario.”

Moreover, the tilt of these objects could not be attributed to the existence of Planet 9, who’s existence has also been suggested based on the extreme eccentricity of certain populations of KBOs. Compared to this Mars-sized planet that is thought to orbit at 60 AUs from the Sun, Planet 9 is predicted to be much more massive (at around 10 Earth masses) and is believed to orbit at a distance of 500 to 700 AU.

Naturally, one has to ask why this planetary-mass body has not been found yet. According to Volk and Malhotra, the reason has to do with the fact that astronomers have not yet searched the entire sky for distant for Solar System objects. Beyond that, there’s also the likely position of the object (within the galactic plane), which is so densely packed with stars that surveys would have a hard time spotting it.



However, with the construction of instruments like the Large Synoptic Survey Telescope (LSST) in Chile nearly complete, opportunities to spot it may be coming sooner other than later. This wide-field survey reflecting telescope, which is run by a consortium that includes the University of Arizona, is expected to provide some of the deepest and widest views of the Universe to date (which will begin in 2020).

In the meantime, and in response to any possible controversies regarding the so-called “Planet Debate”, it is worth noting that this body (if it exists) is currently being referred to as “planetary-mass object”. This is because, by definition, a body needs to have cleared its orbit in order to be called a planet. What’s more, the study does not rule out the possibility that the warp could be the result of more than one planetary mass object in the area.

Therefore, it would premature to state that astronomers – having not yet even confirmed the existence of Planet 9 – are now talking about the existence of a possible “Planet 10”. In the coming years, more news and information will become available, which will hopefully help us put the debate to rest and agree on just how many planets there are out there!

Further Reading: UA News, Earth and Planetary Astrophysics

The post What Caused the Kuiper Belt to Get Warped? appeared first on Universe Today.

Amazing New Views of Betelgeuse Courtesy of ALMA

Amazing New Views of Betelgeuse Courtesy of ALMA:

This orange blob is the nearby star Betelgeuse, as imaged recently by the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA/ESO/NRAO

Just. Wow.

An angry monster lurks in the shoulder of the Hunter. We’re talking about the red giant star Betelgeuse, also known as Alpha Orionis in the constellation Orion. Recently, the Atacama Large Millimeter Array (ALMA) gave us an amazing view of Betelgeuse, one of the very few stars that is large enough to be resolved as anything more than a point of light.

Located 650 light years distant, Betelgeuse is destined to live fast, and die young. The star is only eight million years old – young as stars go. Consider, for instance, our own Sun, which has been shining as a Main Sequence star for more than 500 times longer at 4.6 billion years – and already, the star is destined to go supernova at anytime in the next few thousand years or so, again, in a cosmic blink of an eye.

Still lumpy… Betelgeuse imaged by Hubble in 1996. Hubble/ESA/STScI

An estimated 12 times as massive as Sol, Betelgeuse is perhaps a staggering 6 AU or half a billion miles in diameter; plop it down in the center of our solar system, and the star might extend out past the orbit of Jupiter.

As with many astronomical images, the wow factor comes from knowing just what you’re seeing. The orange blob in the image is the hot roiling chromosphere of Betelgeuse, as viewed via ALMA at sub-millimeter wavelengths. Though massive, the star only appears 50 milliarcseconds across as seen from the Earth. To give you some idea just how small a milliarcsecond is, there’s a thousand of them in an arc second, and 60 arc seconds in an arc minute. The average Full Moon is 30 arc minutes across, or 1.8 million milliarcseconds in apparent diameter. Betelgeuse has one of the largest apparent diameters of any star in our night sky, exceeded only by R Doradus at 57 milliarcseconds.

The apparent diameter of Betelgeuse was first measured by Albert Michelson using the Mount Wilson 100-inch in 1920, who obtained an initial value of 240 million miles in diameter, about half the present accepted value, not a bad first attempt.

You can see hints of an asymmetrical bubble roiling across the surface of Betelgeuse in the ALMA image. Betelgeuse rotates once every 8.4 years. What’s going on under that uneasy surface? Infrared surveys show that the star is enveloped in an enormous bow-shock, a powder-keg of a star that will one day provide the Earth with an amazing light show.

The bowshock created by Betelgeuse as it plows through the local interstellar medium. JAXA/Akari

Thankfully, Betelgeuse is well out of the supernova “kill zone” of 25 to 100 light years (depending on the study). Along with Spica at 250 light years distant in the constellation Virgo, both are prime nearby supernovae candidates that will on day give astronomers a chance to study the anatomy of a supernova explosion up close. Riding high to the south in the northern hemisphere nighttime sky in the wintertime, +0.5 magnitude Betelgeuse would most likely flare up to negative magnitudes and would easily be visible in the daytime if it popped off in the Spring or Fall. This time of year in June would be the worst, as Alpha Orionis only lies 15 degrees from the Sun!

An early springtime supernova in the future? Stellarium

Of course, this cosmic spectacle could kick off tomorrow… or thousands of years from now. Maybe, the light of Betelgeuse gone supernova is already on its way now, traversing the 650 light years of open space. Ironically, the last naked eye supernova in our galaxy – Kepler’s Star in the constellation Ophiuchus in 1604 – kicked off just before Galileo first turned his crude telescope towards the heavens in 1610.

You could say we’re due.

The post Amazing New Views of Betelgeuse Courtesy of ALMA appeared first on Universe Today.

What is the Smallest Planet in the Solar System?

What is the Smallest Planet in the Solar System?:

The Solar Planets are a nice mixed bag of what is possible when it comes to planetary formation. Within the inner Solar System, you have the terrestrial planets – bodies that are composed primarily of silicate minerals and metals. And in the outer Solar System, you have the gas giants and bodies that are composed primarily of ice that lie just beyond in the Trans-Neptunian region.

Of these, the question of which planet is the smallest has been the subject of some controversy. Until recently, the smallest planet was considered to be Pluto. But with the 2006 IAU Resolution that put constraints on what the definition of a planet entails, that status has since passed to Mercury. So in addition to being the closest planet to the Sun, Mercury is also the smallest.

Size and Mass:

With a mean radius of 2440 km, Mercury is the smallest planet in our Solar System, equivalent in size to 0.38 Earths. And given that it has its experiences no flattening at the poles – like Venus, which means it is an almost perfectly spherical body – its radius is the same at the poles as it is the equator.

And while it is smaller than the largest natural satellites in our Solar System – such as Ganymede and Titan – it is more massive. At 3.3011×10²³ kg in mass (33 trillion trillion metric tons; 36.3 trillion trillion US tons), it is equivalent to 0.055 Earths in terms of mass.

Mercury and Earth, size comparison. Credit: NASA / APL (from MESSENGER)

Density, Volume:

On top of that, Mercury is significantly more dense than bodies its size. In fact, Mercury’s density (at 5.427 g/cm³) is the second highest in the Solar System, only slightly less than Earth’s (5.515 g/cm³). The result of this is a gravitational force of 3.7 m/s², which is 0.38 times that of Earth (0.38 g). In essence, this means that if you could stand on the surface of Mercury, you would weight 38% as much as you do on Earth.

In terms of volume, Mercury once again becomes a bit diminutive, at least by Earth standards. Basically, Mercury has a volume of 6.083×10¹⁰ km³ (60 trillion cubic km; 14.39 trillion cubic miles) which works out to 0.056 times the volume of the Earth. In other words, you could fit Mercury inside Earth almost twenty times over.

Structure and Composition:

Like Earth, Venus and Mars, Mercury is a terrestrial planet, meaning that is primarily composed of silicate minerals and metals that are differentiated between a metallic core and a silicate mantle and crust. But in Mercury’s case, the core is oversized compared to the other terrestrial planets, measuring some 1,800 km (approx. 1,118.5 mi) in radius, and therefore occupying 42% of the planet’s volume (compared to Earth’s 17%).

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

Another interesting feature about Mercury’s core is the fact that it 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, leaving behind the core as a major component.

Beyond the core is a mantle that measures 500 – 700 km (310 – 435 mi) in thickness and is composed primarily of silicate material. The outermost layer is Mercury’s crust, which is composed of silicate material that is believed to be 100 – 300 km thick.

Yes, Mercury is a pretty small customer when compared to its brothers, sisters and distant cousins in the Solar System. However, it is also one of the densest, hottest and most irradiated. So while small, no one would ever accuse this planet of not being really tough!

We have written many interesting articles on Mercury and the Solar Planets here at Universe Today. Here’s What is the Biggest Planet in the Solar System?, What is the Second Largest Planet in the Solar System?, How Does Mercury Compare to Earth?, What is the Average Surface Temperature on Mercury?, How Long is a Day on Mercury?, and The Orbit of Mercury, How Long is a Year on Mercury?,

And here’s another take on the smallest planet in the Solar System, and here’s a link to NASA’s Solar System Exploration Guide.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast.

Sources:

• NASA: Solar System Exploration – Mercury
• Wikipedia – Mercury
• Views of the Solar System – Mercury

The post What is the Smallest Planet in the Solar System? appeared first on Universe Today.

Beneath Jupiter

Beneath Jupiter:

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2017 May 29

Explanation: Jupiter is stranger than we knew. NASA's Juno spacecraft has now completed its sixth swoop past Jupiter as it moves around its highly elliptical orbit. Pictured, Jupiter is seen from below where, surprisingly, the horizontal bands that cover most of the planet disappear into swirls and complex patterns. A line of white oval clouds is visible nearer to the equator. Recent results from Juno show that Jupiter's weather phenomena can extend deep below its cloud tops, and that Jupiter's magnetic field varies greatly with location. Juno is scheduled to orbit Jupiter 37 times with each orbit taking about six weeks.

Approaching the Bubble Nebula

Approaching the Bubble Nebula:

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2017 May 31


Approaching the Bubble Nebula

Visualization Credit: NASA, ESA, and F. Summers, G. Bacon, Z. Levay, and L. Frattare (Viz 3D Team, STScI);

Acknowledgment: T. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF, NASA, ESA, and the Hubble Heritage Team (STScI/AURA)


Explanation: What would it look like to approach the Bubble Nebula? Blown by the wind and radiation from a massive star, this bubble now spans seven light-years in diameter. The hot star inside is thousands of times more luminous than our Sun, and is now offset from the nebula's center. The visualization starts with a direct approach toward the Bubble Nebula (NGC 7635) and then moves around the nebula while continuing the approach. The featured time-lapse visualization is extrapolated from images with the orbiting Hubble Space Telescope and the WIYN telescope on Kitt Peak in Arizona, USA. The 3D-computer model on which this visualization is based includes artistic interpretations, and distances are significantly compressed.

Tomorrow's picture: drone's eye view

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Black Holes of Known Mass

Black Holes of Known Mass:

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2017 June 2

Explanation: Add GW170104 to the chart of black holes with known mass. The extremely energetic merger of two smaller black holes corresponds to the Laser Interferometer Gravitational-wave Observatory's (LIGO) third detection of gravitational waves. The newfound black hole has a mass about 49 times that of the Sun, filling a gap between the masses of the two merged black holes detected previously by LIGO, with solar masses of 62 (GW150914) and 21 (GW151226). In all three cases, the signal in each of the twin LIGO detectors was unambiguously identified as coming from black hole mergers while a fourth case (LVT151012) resulted in a lower confidence detection. GW170104 is estimated to be some 3 billion light-years away, more distant than present estimates for GW150914 and GW151226. The ripples in spacetime were discovered during LIGO's current observing run, which began November 30, 2016 and will continue through the summer.