stars Archives

November 14, 2012December 23, 2015 by Jason Major

Closely-Orbiting Stellar Companions Surrounded by “Mystery Dust”

Artist’s concept showing a dust disk around a binary system containing a white dwarf and a less-massive M (red) dwarf companion. (P. Marenfeld and NOAO/AURA/NSF)

Even though NASA’s Wide-field Infrared Survey Explorer spacecraft — aka WISE — ran out of coolant in October 2010, bringing its infrared survey mission to an end, the data that it gathered will be used by astronomers for decades to come as it holds clues to some of the most intriguing and hard-to-find objects in the Universe.

Recently astronomers using WISE data have found evidence of a particularly curious disk of dust and gas surrounding a pair of stars — one a dim red dwarf and the other the remains of a dead Sun-sized star — a white dwarf. The origin of the gas is a mystery, since based on standard models of stellar evolution it shouldn’t be there… yet there it is.

The binary system (which has the easy-to-remember name SDSS J0303+0054) consists of a white dwarf and a red dwarf separated by a distance only slightly larger than the radius of the Sun — about 700,000 km — which is incredibly close for two whole stars. The stars orbit each other quickly too: once every 3 hours.

The stars are so close that the system is referred to as a “post-common envelope” binary, because at one point the outer material of one star expanded out far enough to briefly engulf the other completely in what’s called a “common envelope.” This envelope of material brought the stars even closer together, transferring stellar material between them and ultimately speeding up the death of the white dwarf.

The system was first spotted during the Sloan Digital Sky Survey (hence the SDSS prefix) and was observed with WISE’s infrared abilities during a search for dust disks or brown dwarfs orbiting white dwarf stars. To find both a red (M) dwarf star 40-50 times the mass of Jupiter and a disk of dust orbiting the white dwarf in this system was unexpected — in fact, it’s the only known example of a system like it.

The entire mass of the dust (termed an infrared excess) is estimated to be “equivalent to the mass of an asteroid a few tens of kilometers in radius” and extends out to about the same distance as Venus’ orbit — just over 108 million kilometers, or 0.8 AU.

Why is the dust so unusual? Because, basically, it shouldn’t even be there. At that distance from the white dwarf, positioned just out of reach (but not terribly far away at all) anything that was within that zone when the original Sun-sized star swelled into its red giant phase should have spiraled inwards, getting swallowed up by the expanding stellar atmosphere.

Such is the fate that likely awaits the inner planets of our own Solar System — including Earth — when the Sun reaches the final phases of its stellar life.

So this requires that there are other sources of the dust. According to the WISE science update, “One possibility is that it is caused by multiple asteroids that orbit further away and somehow are perturbed close to the binary and collide with each other. [Another] is that the red dwarf companion releases a large amount of gas in a stellar wind that is trapped by the gravitational pull of its more massive white dwarf companion. The gas then condenses and forms the dust disk that is observed.

“Either way, this new discovery provides an interesting laboratory for the study of binary star evolution.”

See the team’s paper here, and read more on Berkeley’s WISE mission site here.

WISE launched into space on Dec. 14, 2009 on a mission to map the entire sky in infrared light with greatly improved sensitivity and resolution over its predecessors. From its polar orbit 525 kilometers (326 miles) in altitude it scanned the skies, collecting images taken at four infrared wavelengths of light. WISE took more than 2.7 million images over the course of its mission, capturing objects ranging from faraway galaxies to asteroids relatively close to Earth before exhausting the supply of coolant necessary to mask its own heat from its ultra-sensitive sensors.

Inset: Infrared images of SDSS J0303+0054. (NASA/JPL and John H. Debes et. al.)

October 5, 2012December 23, 2015 by Nancy Atkinson

Two Stars Do a Short-Orbit Tango Around the Milky Way’s Black Hole

Astronomers have known for some time there was one star orbiting fairly close to the black hole at the center of our galaxy. But now another star has been found dipping close and orbiting even faster around the Milky Way’s central black hole. Astronomer Andrea Ghez from UCLA says the ability to watch these two stars in a short-period ‘tango’ around the black hole will help scientist measure the effects of space-time curvature, and they should be able to determine whether Albert Einstein was right in his prediction of how black holes could warp space and time.

“I’m extremely pleased to find two stars that orbit our galaxy’s supermassive black hole in much less than a human lifetime,” said Ghez. “It is the tango of [these stars] that will reveal the true geometry of space and time near a black hole for the first time. This measurement cannot be done with one star alone.”

There are nearly 3,000 stars that orbit somewhat close to the black hole, and most of them have orbits of 60 years or longer.
The previously known close-in star, S0-2, orbits the black hole every 15.5 years. And now, the newly found star, called S0-102, orbits the black hole in a blazing 11.5 years, the shortest known orbit of any star near this black hole.

Reconstruction of the orbits of two stars—S0-2 and S0-102—near the black hole at the Milky Way’s center. (Other stars’ orbits are also depicted by fainter lines.) The background is a real high-resolution infrared image of the region. Credit: Andrea Ghez et al./UCLA/Keck

In the same way that planets orbit around the sun, S0-102 and S0-2 are each in an elliptical orbit around the central black hole. Ghez said that the planetary motion in our solar system was the ultimate test for Newton’s gravitational theory 300 years ago, and now the motion of S0-102 and S0-2 will be the ultimate test for Einstein’s theory of general relativity, which describes gravity as a consequence of the curvature of space and time.

“The exciting thing about seeing stars go through their complete orbit is not only that you can prove that a black hole exists but you have the first opportunity to test fundamental physics using the motions of these stars,” Ghez said. “Showing that it goes around in an ellipse provides the mass of the supermassive black hole, but if we can improve the precision of the measurements, we can see deviations from a perfect ellipse — which is the signature of general relativity.”

As the stars come to their closest approach, their motion will be affected by the curvature of spacetime, and the light traveling from the stars to us will be distorted, Ghez said.

S0-2, which is 15 times brighter than S0-102, will go through its closest approach to the black hole in 2018. S0-102 makes its closest approach in 2021, so the team will be keeping an eye on these stars as they get tantalizingly close, but not close enough to get sucked in, Ghez said.

Ghez and her colleagues have been observing S0-2 since 1995. In 2000, she and her team reported — for the first time – that astronomers had seen stars accelerate around the supermassive black hole. Their research demonstrated that three stars had accelerated by more than 250,000 mph a year as they orbited the black hole. The speed of S0-102 and S0-2 should also accelerate by more than 250,000 mph at their closest approach, Ghez said.

“The fact that we can find stars that are so close to the black hole is phenomenal,” said Ghez. “Now it’s a whole new ballgame, in terms of the kinds of experiments we can do to understand how black holes grow over time, the role supermassive black holes play in the center of galaxies, and whether Einstein’s theory of general relativity is valid near a black hole, where this theory has never been tested before. It’s exciting to now have a means to open up this window.”

The research was done using the Keck Telescopes. The team’s paper was published Oct. 5 in the journal Science.

Source: UCLA

Lead image caption: The Keck I and Keck II telescopes focus on two stars orbiting Milky Way’s black hole. Background photo credit: Dan Birchall/Subaru Telescope on Mauna Kea, Hawaii. Overlay created by Professor Andrea Ghez and her research team at UCLA and are from data sets obtained with the W. M. Keck Telescopes.

August 29, 2012December 23, 2015 by Jason Major

Effects of Einstein’s Elusive Gravitational Waves Observed

Chandra data (above, graph) on J0806 show that its X-rays vary with a period of 321.5 seconds, or slightly more than five minutes. This implies that the X-ray source is a binary star system where two white dwarf stars are orbiting each other (above, illustration) only 50,000 miles apart, making it one of the smallest known binary orbits in the Galaxy. According to Einstein's General Theory of Relativity, such a system should produce gravitational waves - ripples in space-time - that carry energy away from the system and cause the stars to move closer together. X-ray and optical observations indicate that the orbital period of this system is decreasing by 1.2 milliseconds every year, which means that the stars are moving closer at a rate of 2 feet per year. — Potential stellar collision. Credit: Chandra

Two white dwarfs similar to those in the system SDSS J065133.338+284423.37 spiral together in this illustration from NASA. Credit: D. Berry/NASA GSFC

Locked in a spiraling orbital embrace, the super-dense remains of two dead stars are giving astronomers the evidence needed to confirm one of Einstein’s predictions about the Universe.

A binary system located about 3,000 light-years away, SDSS J065133.338+284423.37 (J0651 for short) contains two white dwarfs orbiting each other rapidly — once every 12.75 minutes. The system was discovered in April 2011, and since then astronomers have had their eyes — and four separate telescopes in locations around the world — on it to see if gravitational effects first predicted by Einstein could be seen.

According to Einstein, space-time is a structure in itself, in which all cosmic objects — planets, stars, galaxies — reside. Every object with mass puts a “dent” in this structure in all dimensions; the more massive an object, the “deeper” the dent. Light energy travels in a straight line, but when it encounters these dents it can dip in and veer off-course, an effect we see from Earth as gravitational lensing.

Einstein also predicted that exceptionally massive, rapidly rotating objects — such as a white dwarf binary pair — would create outwardly-expanding ripples in space-time that would ultimately “steal” kinetic energy from the objects themselves. These gravitational waves would be very subtle, yet in theory, observable.

Read: Astronomy Without a Telescope: Gravitational Waves

What researchers led by a team at The University of Texas at Austin have found is optical evidence of gravitational waves slowing down the stars in J0651. Originally observed in 2011 eclipsing each other (as seen from Earth) once every six minutes, the stars now eclipse six seconds sooner. This equates to a predicted orbital period reduction of about 0.25 milliseconds each year.*

“These compact stars are orbiting each other so closely that we have been able to observe the usually negligible influence of gravitational waves using a relatively simple camera on a 75-year-old telescope in just 13 months,” said study lead author J.J. Hermes, a graduate student at The University of Texas at Austin.

Based on these measurements, by April 2013 the stars will be eclipsing each other 20 seconds sooner than first observed. Eventually they will merge together entirely.

Although this isn’t “direct” observation of gravitational waves, it is evidence inferred by their predicted effects… akin to watching a floating lantern in a dark pond at night moving up and down and deducing that there are waves present.

“It’s exciting to confirm predictions Einstein made nearly a century ago by watching two stars bobbing in the wake caused by their sheer mass,” said Hermes.

As of early last year NASA and ESA had a proposed mission called LISA (Laser Interferometer Space Antenna) that would have put a series of 3 detectors into space 5 million km apart, connected by lasers. This arrangement of precision-positioned spacecraft could have detected any passing gravitational waves in the local space-time neighborhood, making direct observation possible. Sadly this mission was canceled due to FY2012 budget cuts for NASA, but ESA is moving ahead with developments for its own gravitational wave mission, called eLISA/NGO — the first “pathfinder” portion of which is slated to launch in 2014.

The study was submitted to Astrophysical Journal Letters on August 24. Read more on the McDonald Observatory news release here.

Inset image: simulation of binary black holes causing gravitational waves – C. Reisswig, L. Rezzolla (AEI); Scientific visualization – M. Koppitz (AEI & Zuse Institute Berlin)

*The difference in the eclipse time is noted as six seconds even though the orbital period decay of the two stars is only .25 milliseconds/year because of a pile-up effect of all the eclipses observed since April 2011. The measurements made by the research team takes into consideration the phase change in the J0651 system, which experiences a piling effect — similar to an out-of-sync watch — that increases relative to time^2 and is therefore a larger and easier number to detect and work with. Once that was measured, the actual orbital period decay could be figured out.

July 26, 2012December 23, 2015 by Nancy Atkinson

Bright Stars Don’t Like to Be Alone

Caption: New research using data from European Southern Observatory telescopes, including the Very Large Telescope, has revealed that the hottest and brightest stars, known as O stars, are often found in close pairs. Credit: ESA, NASA, H. Sana (Amsterdam University), and S.E. de Mink (STScI)

Like humans, stars seem to prefer the company of companions. A new study using the Very Large Telescope reveals that most very bright, high-mass O-type stars do not live alone. Surprisingly, almost three-quarters of these stars have a close companion star, far more than previously thought. But sometimes – also like humans – the relationship between companion stars can turn a little ugly, with one star becoming dominant and even disruptive by stealing matter from the other, or doing a hostile takeover.

An international team of astronomers have found that some stars will virtually suck the life out of another, and about one-third of the time, a pair of stars will ultimately merge to form a single star.

The stars included in this study are some of the biggest, brightest stars which have very high temperatures. They live fast and die young, and in their lives play a key role in the evolution of galaxies. by, which drive the evolution of galaxies. They are also linked to extreme phenomena such as gamma-ray bursts.

“These stars are absolute behemoths,” said Hugues Sana, from the University of Amsterdam, The Netherlands, lead author of the study. “They have 15 or more times the mass of our Sun and can be up to a million times brighter. These stars are so hot that they shine with a brilliant blue-white light and have surface temperatures over 54,000 degrees Fahrenheit (30,000 degrees C).”

The astronomers studied a sample of 71 O-type single stars and stars in pairs (binaries) in six nearby young star clusters in the Milky Way.
By analyzing the light coming from these targets in greater detail than before, the team discovered that 75 percent of all O-type stars exist inside binary systems, a higher proportion than previously thought, and the first precise determination of this number. More importantly, though, they found that the proportion of these pairs that are close enough to interact (through stellar mergers or transfer of mass by so-called vampire stars) is far higher than anyone had thought, which has profound implications for our understanding of galaxy evolution.

O-type stars make up just a fraction of a percent of the stars in the universe, but the violent phenomena associated with them mean they have a disproportionate effect on their surroundings. The winds and shocks coming from these stars can both trigger and stop star formation, their radiation powers the glow of bright nebulae, their supernovae enrich galaxies with the heavy elements crucial for life, and they are associated with gamma-ray bursts, which are among the most energetic phenomena in the universe. O-type stars are therefore implicated in many of the mechanisms that drive the evolution of galaxies.

“The life of a star is greatly affected if it exists alongside another star,” said Selma de Mink of the Space Telescope Science Institute, in Baltimore, Md., a co-author of the study. “If two stars orbit very close to each other they may eventually merge. But even if they don’t, one star will often pull matter off the surface of its neighbor.”

Mergers between stars, which the team estimates will be the ultimate fate of around 20 to 30 percent of O-type stars, are violent events. But even the comparatively gentle scenario of vampire stars, which accounts for a further 40 to 50 percent of cases, has profound effects on how these stars evolve.

Until now, astronomers mostly considered that closely orbiting massive binary stars were the exception, something that was only needed to explain exotic phenomena such as X-ray binaries, double pulsars, and black hole binaries. The new study shows that to properly interpret the universe, this simplification cannot be made: these heavyweight double stars are not just common, their lives are fundamentally different from those of single stars.

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For instance, in the case of vampire stars — where the smaller, lower-mass star is rejuvenated as it sucks the fresh hydrogen from its companion — its mass will increase substantially and it will outlive its companion, surviving much longer than a single star of the same mass. The victim star, meanwhile, is stripped of its envelope before it has a chance to become a luminous red supergiant. Instead, its hot, blue core is exposed. As a result, the stellar population of a distant galaxy may appear to be much younger than it really is: both the rejuvenated vampire stars, and the diminished victim stars become hotter, and bluer in color, mimicking the appearance of younger stars. Knowing the true proportion of interacting high-mass binary stars is therefore crucial to correctly characterize these faraway galaxies.

“The only information astronomers have on distant galaxies is from the light that reaches our telescopes. Without making assumptions about what is responsible for this light we cannot draw conclusions about the galaxy, such as how massive or how young it is. This study shows that the frequent assumption that most stars are single can lead to the wrong conclusions,” said Sana.

Understanding how big these effects are, and how much this new perspective will change our view of galactic evolution, will need further work. Modeling binary stars is complicated, so it will take time before all these considerations are included in models of galaxy formation.

The paper was published in the July 27 issue of the journal Science.

Paper by: Sana, de Mink, et al. (PDF document)

Sources: ESO, HubbleSite

July 5, 2012December 23, 2015 by Jason Major

WISE Spies a Hunter’s Flame

A vast star-forming cloud of gas and dust in the constellation Orion shines brightly in this image from NASA’s WISE space telescope, where infrared light is represented in visible wavelengths. It’s part of a recent data release from WISE, a trove of infrared images acquired during the telescope’s second sky scan from August to September of 2010 — just as it began to run out of its essential cryogenic coolant.

Shining brightly in infrared radiation, the Flame nebula (NGC 2024) is at the heart of the cloud. Just below it is the reflection nebula NGC 2023, and the small, bright loop protruding from the edge of the gas and dust cloud just to its lower right is the Horsehead nebula — whose famous equine profile appears quite different in infrared light than it does in visible.

The two bright blue stars at the upper right portion of the image are both stars in Orion’s belt. Alnitak, the brighter one closer to the Flame nebula, is a multiple star system located 736 light-years away whose stellar wind is responsible for ionizing the Flame nebula and causing it to shine in infrared. Alnilam, the dimmer star at the uppermost corner, is a blue supergiant 24 times the radius of our Sun and 275,000 times as bright, but 1,980 light-years distant.

The red arc at lower right is the bow shock of Sigma Orionis, a multiple-star system that’s hurtling through space at a speed of 5,260,000 mph (2,400 kilometers per second). As its stellar wind impacts the interstellar medium and piles up before it, an arc of infrared-bright radiation is emitted.

Sigma Orionis is also the star responsible for the glow of the Horsehead nebula.

This rich astronomical scene is an expanded view from WISE’s previously-released image of the region (at right) which used data from only three of its four infrared detectors. In contrast, all four detectors were used in the image above, making more of the nebulae’s intricate structures visible as well as providing comparative information for researchers.

“If you’re an astronomer, then you’ll probably be in hog heaven when it comes to infrared data,” said Edward (Ned) Wright of UCLA, the principal investigator of the WISE mission. “Data from the second sky scan are useful for studying stars that vary or move over time, and for improving and checking data from the first scan.”

Read more on the NASA news release here.

Top and right images: NASA/JPL-Caltech/WISE team. Horsehead nebula visible light image was taken with the 0.9-meter telescope at Kitt Peak National Observatory. Photo credit & copyright: Nigel Sharp (NOAO), KPNO, AURA, NSF. Comparison by J. Major/Universe Today.

June 27, 2012December 23, 2015 by Jason Major

How to Measure a Hot Jupiter

An international team of astronomers has figured out a way to determine details of an exoplanet’s atmosphere from 50 light-years away… even though the planet doesn’t transit the face of its star as seen from Earth.

Tau Boötis b is a “hot Jupiter” type of exoplanet, 6 times more massive than Jupiter. It was the first planet to be identified orbiting its parent star, Tau Boötis, located 50 light-years away. It’s also one of the first exoplanets we’ve known about, discovered in 1996 via the radial velocity method — that is, Tau Boötis b exerts a slight tug on its star, shifting its position enough to be detectable from Earth. But the exoplanet doesn’t pass in front of its star like some others do, which until now made measurements of its atmosphere impossible.

Today, an international team of scientists working with the Very Large Telescope (VLT) at ESO’s Paranal Observatory in Chile have announced the success of a “clever new trick” of examining such non-transiting exoplanet atmospheres. By gathering high-quality infrared observations of the Tau Boötis system with the VLT’s CRIRES instrument the researchers were able to differentiate the radiation coming from the planet versus that emitted by its star, allowing the velocity and mass of Tau Boötis b to be determined.

“Thanks to the high quality observations provided by the VLT and CRIRES we were able to study the spectrum of the system in much more detail than has been possible before,” said Ignas Snellen with Leiden Observatory in the Netherlands, co-author of the research paper. “Only about 0.01% of the light we see comes from the planet, and the rest from the star, so this was not easy.”

Using this technique, the researchers determined that Tau Boötis b’s thick atmosphere contains carbon monoxide and, curiously, exhibits cooler temperatures at higher altitudes — the opposite of what’s been found on other hot Jupiter exoplanets.

“Maybe one day we may even find evidence for biological activity on Earth-like planets in this way.”

– Ignas Snellen, Leiden Observatory, the Netherlands

In addition to atmospheric details, the team was also able to use the new method to determine Tau Boötis b’s mass and orbital angle — 44 degrees, another detail not previously identifiable.

“The new technique also means that we can now study the atmospheres of exoplanets that don’t transit their stars, as well as measuring their masses accurately, which was impossible before,” said Snellen. “This is a big step forward.

“Maybe one day we may even find evidence for biological activity on Earth-like planets in this way.”

This research was presented in a paper “The signature of orbital motion from the dayside of the planet Tau Boötis b”, to appear in the journal Nature on June 28, 2012.

Milky Way to Concordia Base… Come In, Concordia Base…

This stunning photo of the Milky Way was captured from what may be the coldest and most isolated research facility on Earth: the French-Italian Concordia Base station, located at 3,200 meters (nearly 10,500 feet) altitude on the Antarctic plateau, 1,670 km (1,037 miles) from the geographic south pole.

Taken by Dr. Alexander Kumar, a doctor, researcher and photographer who’s been living at the Base since January, the image shows the full beauty of the sky above the southern continent — a sky that doesn’t see the Sun from May to August.

During the winter months no transportation can be made to or from Concordia Base — no deliveries or evacuations, not for any reason. The team there is truly alone, very much like future space explorers will one day be. This isolation is one reason that Concordia is used by ESA for research for missions to Mars.

Of course, taking photos outside is no easy task. Temperatures outside the Base in winter can drop down to -70ºC (-100ºF)!

Still, despite the isolation, darkness and cold, Dr. Kumar finds inspiration in his surroundings.

“The dark may cause fear, but if you take the time to adapt and look within it, you never know what you may find – at the bottom of the ocean, in the night sky, or under your bed in the middle of the night,” writes Kumar on the Concordia blog. “If you don’t overcome your fear of the ‘unknown’ and ‘monsters’, you will never see marvellous secrets hidden in the dark.

“I hope this photo inspires you too for the days, weeks and months ahead. In terms of the space exploration we are only beginning. We have to continue pushing out into the great beyond.”

Image credits: ESA/IPEV/PNRA – A. Kumar

May 16, 2012December 23, 2015 by Jason Major

The Big Dipper Like You’ve Never Seen It Before!

Junocam image of the stars that make up the "Big Dipper" asterism

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All right, it may look just like any other picture you’ve ever seen of the Big Dipper. Maybe even a little less impressive, in fact. But, unlike any other picture, this one was taken from 290 million km away by NASA’s Juno spacecraft en route to Jupiter, part of a test of its Junocam instrument! Now that’s something new concerning a very old lineup of stars!

“I can recall as a kid making an imaginary line from the two stars that make up the right side of the Big Dipper’s bowl and extending it upward to find the North Star,” said Scott Bolton, principal investigator of NASA’s Juno mission. “Now, the Big Dipper is helping me make sure the camera aboard Juno is ready to do its job.”

567922main_junospacecraft0711 — Diagram of the Juno spacecraft (NASA/JPL)

The image is a section of a larger series of scans acquired by Junocam between 20:23 and 20:56 UTC (3:13 to 3:16 PM EST) on March 14, 2012. Still nowhere near Jupiter, the purpose of the imaging exercise was to make sure that Junocam doesn’t create any electromagnetic interference that could disrupt Juno’s other science instruments.

In addition, it allowed the Junocam team at Malin Space Science Systems in San Diego, CA to test the instrument’s Time-Delay Integration (TDI) mode, which allows image stabilization while the spacecraft is in motion.

Because Juno is rotating at about 1 RPM, TDI is crucial to obtaining focused images. The images that make up the full-size series of scans were taken with an exposure time of 0.5 seconds, and yet the stars (brightened above by the imaging team) are still reasonably sharp… which is exactly what the Junocam team was hoping for.

“An amateur astrophotographer wouldn’t be very impressed by these images, but they show that Junocam is correctly aligned and working just as we expected”, said Mike Caplinger, Junocam systems engineer.

As well as the Big Dipper, Junocam also captured other stars and asterisms, such as Vega, Canopus, Regulus and the “False Cross”. (Portions of the imaging swaths were also washed out by sunlight but this was anticipated by the team.)

These images will be used to further calibrate Junocam for operation in the low-light environment around Jupiter, once Juno arrives in July 2016.

Read more about the Junocam test on the MSSS news page here.

As of May 10, Juno was approximately 251 million miles (404 million kilometers) from Earth. Juno has now traveled 380 million miles (612 million kilometers) since its launch on August 5, 2011 and is currently traveling at a velocity of 38,300 miles (61,600 kilometers) per hour relative to the Sun.

Watch a video of the Juno launch here, taken by yours truly from the press site at Kennedy Space Center!

May 14, 2012December 23, 2015 by Jason Major

A Sword of Stars

The stars and dust of spiral galaxy NGC 891 seen by Hubble edge-on

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Like the blade of a magical weapon from a fantasy tale, the northern edge of spiral galaxy NGC 891 is captured by the Hubble Space Telescope, glowing with the light of billions of stars and interwoven with dark clouds of dust and cold gas.

In reality this cosmic blade is enormous. About the same size as our galaxy, NGC 891 is approximately 100,000 light-years in diameter, making the section visible here around 40,000 light-years in length.

Unlike the Milky Way, however, NGC 891 is unbarred and also exhibits many more filaments of dark gas and dust. Astronomers suggest that these are the result of star formation and supernovae, both of which can expel vast amounts of interstellar material far out into space.

The few bright stars in the foreground are located in our own galaxy.

NGC 891 is located in the constellation Andromeda and lies about 30 million light-years away… that means the light captured by Hubble’s Advanced Camera for Surveys to create the image above began its journey 35 million years after the asteroid impact that led to the extinction of the dinosaurs, and about 26 million years before our ancient African ancestors began walking upright. That may sound like a long trip but, as Douglas Adams so eloquently said, “that’s just peanuts to space!”

The Secret Origin Story of Brown Dwarfs

Artist's impression of a Y-dwarf, the coldest known type of brown dwarf star. (NASA/JPL-Caltech)

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Sometimes called failed stars, brown dwarfs straddle the line between star and planet. Too massive to be “just” a planet, but lacking enough material to start fusion and become a full-fledged star, brown dwarfs are sort of the middle child of cosmic objects. Only first detected in the 1990s, their origins have been a mystery for astronomers. But a researchers from Canada and Austria now think they have an answer for the question: where do brown dwarfs come from?

If there’s enough mass in a cloud of cosmic material to start falling in upon itself, gradually spinning and collapsing under its own gravity to compress and form a star, why are there brown dwarfs? They’re not merely oversized planets — they aren’t in orbit around a star. They’re not stars that “cooled off” — those are white dwarfs (and are something else entirely.) The material that makes up a brown dwarf probably shouldn’t have even had enough mass and angular momentum to start the whole process off to begin with, yet they’re out there… and, as astronomers are finding out now that they know how to look for them, there’s quite a lot.

So how did they form?

According to research by Shantanu Basu of the University of Western Ontario and Eduard I. Vorobyov from the University of Vienna in Austria and Russia’s Southern Federal University, brown dwarfs may have been flung out of other protostellar disks as they were forming, taking clumps of material with them to complete their development.

Basu and Vorobyov modeled the dynamics of protostellar disks, the clouds of gas and dust that form “real” stars. (Our own solar system formed from one such disk nearly five billion years ago.) What they found was that given enough angular momentum — that is, spin — the disk could easily eject larger clumps of material while still having enough left over to eventually form a star.

Basu-Vorobyov model — Model of how a clump of low-mass material gets ejected from a disk (S. Basu/E. Vorobyev)

The ejected clumps would then continue condensing into a massive object, but never quite enough to begin hydrogen fusion. Rather than stars, they become brown dwarfs — still radiating heat but nothing like a true star. (And they’re not really brown, by the way… they’re probably more of a dull red.)

In fact a single protostellar disk could eject more than one clump during its development, Basu and Vorobyov found, leading to the creation of multiple brown dwarfs.

If this scenario is indeed the way brown dwarfs form, it stands to reason that the Universe may be full of them. Since they are not very luminous and difficult to detect at long distances, the researchers suggest that brown dwarfs may be part of the answer to the dark matter mystery.

“There could be significant mass in the universe that is locked up in brown dwarfs and contribute at least part of the budget for the universe’s missing dark matter,” Basu said. “And the common idea that the first stars in the early universe were only of very high mass may also need revision.”

Based on this hypothesis, with the potential number of brown dwarfs that could be in our galaxy alone we may find that these “failed stars” are actually quite successful after all.

The team’s research paper was accepted on March 1 into The Astrophysical Journal.

Read more on the University of Western Ontario’s news release here.