When Is a Star Not a Star?

When it’s a brown dwarf — but where do we draw the line?

Often called “failed stars,” brown dwarfs are curious cosmic creatures. They’re kind of like swollen, super-dense Jupiters, containing huge amounts of matter yet not quite enough to begin fusing hydrogen in their cores. Still, there has to be some sort of specific tipping point, and astronomers (being the scientists that they are) would like to know: when does a brown dwarf stop and a star begin?

Researchers from Georgia State University now have the answer.

From a press release issued Dec. 9 from the National Optical Astronomy Observatory (NOAO):

For most of their lives, stars obey a relationship referred to as the main sequence, a relation between luminosity and temperature – which is also a relationship between luminosity and radius. Stars behave like balloons in the sense that adding material to the star causes its radius to increase: in a star the material is the element hydrogen, rather than air which is added to a balloon. Brown dwarfs, on the other hand, are described by different physical laws (referred to as electron degeneracy pressure) than stars and have the opposite behavior. The inner layers of a brown dwarf work much like a spring mattress: adding additional weight on them causes them to shrink. Therefore brown dwarfs actually decrease in size with increasing mass.

Read more: The Secret Origin Story of Brown Dwarfs

As Dr. Sergio Dieterich, the lead author, explained, “In order to distinguish stars from brown dwarfs we measured the light from each object thought to lie close to the stellar/brown dwarf boundary. We also carefully measured the distances to each object. We could then calculate their temperatures and radii using basic physical laws, and found the location of the smallest objects we observed (see the attached illustration, based on a figure in the publication). We see that radius decreases with decreasing temperature, as expected for stars, until we reach a temperature of about 2100K. There we see a gap with no objects, and then the radius starts to increase with decreasing temperature, as we expect for brown dwarfs. “

Dr. Todd Henry, another author, said: “We can now point to a temperature (2100K), radius (8.7% that of our Sun), and luminosity (1/8000 of the Sun) and say ‘the main sequence ends there’ and we can identify a particular star (with the designation 2MASS J0513-1403) as a representative of the smallest stars.”

The relation between size and temperature at the point where stars end and brown dwarfs begin (based on a figure from the publication) Image credit: P. Marenfeld & NOAO/AURA/NSF.
The relation between size and temperature at the point where stars end and brown dwarfs begin (based on a figure from the publication) Image credit: P. Marenfeld & NOAO/AURA/NSF.

“We can now point to a temperature (2100K), radius (8.7% that of our Sun), and luminosity (1/8000 of the Sun) and say ‘the main sequence ends there’.”

Dr. Todd Henry, RECONS Director

Aside from answering a fundamental question in stellar astrophysics about the cool end of the main sequence, the discovery has significant implications in the search for life in the universe. Because brown dwarfs cool on a time scale of only millions of years, planets around brown dwarfs are poor candidates for habitability, whereas very low mass stars provide constant warmth and a low ultraviolet radiation environment for billions of years. Knowing the temperature where the stars end and the brown dwarfs begin should help astronomers decide which objects are candidates for hosting habitable planets.

The data came from the SOAR (SOuthern Astrophysical Research) 4.1-m telescope and the SMARTS (Small and Moderate Aperture Research Telescope System) 0.9-m telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile.

Read more here.

A Cosmic Rose for Your Spacey Valentine

We space-nerds like to express our amorous feelings, just like the rest of the population (although admittedly some of need more help/prodding in this area than others). And so just in time for Valentine’s Day comes this new image of a planetary nebula, which looks like a rose — or even a tulip – to share with your very spacey valentine.

The name of this planetary nebula, however, is not so romantic: Sh2-174. We need some suggestions for a better name!

And the way this object was created is not so romantic, either, as planetary nebulae come about in violent events. Sh2-174 was created when a low-mass star blew off its outer layers at the end of its life. The core of the star remains and is called a white dwarf. Usually the white dwarf can be found very near the center of the planetary nebula. But in the case of Sh2-174 it is off to the right. (It is the very blue star near the center of the blue gas). This asymmetry is due to the planetary nebula’s interaction with the interstellar medium that surrounds it.

This image was obtained with the wide-field view of the National Optical Astronomy Observatory (NOAO) Mosaic 1 camera on the Mayall 4-meter telescope at Kitt Peak National Observatory. Travis Rector from the University of Alaska Anchorage made the observations for this image, taken through four different filters which are assigned colors that approximate what the human eye can see: B (blue), I (orange), Hydrogen-alpha (red) and Oxygen [OIII] (blue) filters. In this image, North is up, East is to the left.

Source: NOAO

One of the Largest Astronomical Images Ever Made

The northern portion of the Cygnus Loop, as seen in an enormous new panorama from the National Optical Astronomy Observatory (NOAO) and WIYN partners

Looking for a stunning new desktop image to wrap up the year? Try this: it’s an amazing panorama of the Cygnus Loop, a supernova remnant located 1,500 light-years away in the constellation (you guessed it) Cygnus. The full-size image, acquired with the wide-field Mosaic camera on the WIYN 0.9-meter telescope at Kitt Peak, Arizona, is a staggering 600 million pixels in size — over 1.68 gigabytes — making it one of the largest astronomical images ever made!

See the full image (and links to download larger versions) below:

2000-pixel-wide version of the full Cygnus Loop panorama

The entire structure of the Cygnus Loop, the gaseous remains of a supernova that occurred 5,000 – 10,000 years ago, covers an area nearly 45 times the size of the full Moon in the sky.

In the image, hydrogen alpha, sulphur, and oxygen ions correspond to the red, green, and blue color values, respectively.

“Images like this are amazing because they can remind you of the big picture and beauty that surrounds us.”

–  Dr. Richard Cool, MMT Observatory

From the NOAO press release:

Astronomers estimate the supernova explosion that produced the nebula occurred between 5,000 to 10,000 years ago. First noted in 1784 by William Herschel, it is so large that its many parts have been catalogued as separate objects, including NGC 6992, NGC 6995 and IC 1340 along the eastern (left) side of the image, NGC 6974 and NGC 6979 near the top-center, and the Veil Nebula (NGC 6960) and Pickering’s Triangle along the western (right) edge. The bright star near the western edge of the image, known as 52 Cygnus, is not associated with the supernova.

“Often, astronomical research reduces images to dry tables of numerical information that we analyze in order to more deeply understand our universe,” said Dr. Richard Cool, astronomer at the MMT Observatory in Arizona, who originally obtained the images in 2003 while still a graduate student. “Images like this are amazing because they can remind you of the big picture and beauty that surrounds us.”

This incredible image demonstrates that even relatively small telescopes are capable of producing cutting-edge research, when equipped with modern cameras.

Got bandwidth to spare? Download the full-size 1686.5 MB TIFF image here, or find other versions on the NOAO page here.

Image Credit: T.A. Rector (University of Alaska Anchorage), Richard Cool (University of Arizona) and WIYN/NOAO/AURA/NSF. Inset image: original dome of the Kitt Peak 0.9-meter telescope. (NOAO/AURA/NSF)

First Images in a New Hunt for Dark Energy

Zoomed-in image from the Dark Energy Camera of the barred spiral galaxy NGC 1365, about 60 million light-years from Earth. (Dark Energy Survey Collaboration)

The ongoing search for dark energy now has a new set of eyes: the Dark Energy Camera, mounted on the 4-meter Victor M. Blanco telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory in Chile. The culmination of eight years of planning and engineering, the phone-booth-sized 570-megapixel Dark Energy Camera has now gathered its very first images, capturing light from cosmic structures tens of millions of light-years away.

Eventually the program’s survey will help astronomers uncover the secrets of dark energy — the enigmatic force suspected to be behind the ongoing and curiously accelerating expansion of the Universe.

Zoomed-in image from the Dark Energy Camera of the Fornax cluster

“The Dark Energy Survey will help us understand why the expansion of the universe is accelerating, rather than slowing due to gravity,” said Brenna Flaugher, project manager and scientist at Fermilab.

Read more: Polar Telescope Casts New Light on Dark Energy

The most powerful instrument of its kind, the Dark Energy Camera will be used to create highly-detailed color images of  a full 1/8th of the night sky — about 5,000 square degrees — surveying thousands of supernovae, galactic clusters and literally hundreds of millions of galaxies, peering as far away as 8 billion light-years.

The survey will attempt to measure the effects of dark energy on large-scale cosmic structures, as well as identify its gravitational lensing effects on light from distant galaxies. The images seen here, acquired on September 12, 2012, are just the beginning… the Dark Energy Survey is expected to begin actual scientific investigations this December.

Full Dark Energy Camera composite image of the Small Magellanic Cloud

“The achievement of first light through the Dark Energy Camera begins a significant new era in our exploration of the cosmic frontier,” said James Siegrist, associate director of science for high energy physics with the U.S. Department of Energy. “The results of this survey will bring us closer to understanding the mystery of dark energy, and what it means for the universe.”

Read more on the Symmetry Magazine article here, and you can also follow the Dark Energy Survey on Facebook here. (The Fermilab press release can be found here.)

Images: Dark Energy Survey Collaboration. Inset image: the 4-meter Blanco Telescope dome at CTIO (NOAO)

The Dark Energy Survey is supported by funding from the U.S. Department of Energy; the National Science Foundation; funding agencies in the United Kingdom, Spain, Brazil, Germany and Switzerland; and the participating DES institutions.

 

With Proposed Cuts, Can the US Continue to be a Leader in Astronomy? Q & A with NOAO Director David Silva

The Kitt Peak Observatory

Last week, a report issued by the National Science Foundation’s Division of Astronomical Sciences suggested de-funding several ground-based observatories along with other money-saving strategies to help offset budget shortfalls in US astronomy which have been projected to be as much as 50%. The report recommended the closure of iconic facilities such as the Very Long Baseline Array (VLBA) and the Green Bank Radio Telescope, as well as shutting down four different telescopes at the Kitt Peak Observatory by 2017.

Universe Today talked with the Director of the National Optical Astronomy Observatory (NOAO), Dr. David Silva for his reactions to the report.

Universe Today: What is your initial reaction to the STP portfolio review:

David Silva: “It’s disappointing, but not completely unexpected. I think the biggest challenge for the overall US community is they’re going to lose access to a lot of world-class, cutting-edge facilities. This is roughly somewhere between eight hundred to a thousand nights of open access time which is going to be defunded over the next three years or so. That’s a huge culture change for US astronomy.

UT: Do you see this affecting the researchers at smaller facilities and universities the most?

Silva: Definitely. Clearly, the situation is now that if you’re at an institution that has its own facility, everything should be OK. But if you’re at an institution that does not have access to its own facility, you’re in a bad situation. So that naturally segregates the bigger universities versus the smaller universities.

I should say there is a caveat, in that we are in an era now in professional astronomy where surveys are now becoming a much stronger component of what we do. Surveys are the big wide-field surveys both from space and from the ground which are producing massive datasets that are open to everyone. So, what’s really happening is this culture change from people having to compete for one or two nights a year on a telescope to potentially working on the big datasets. So, how that transition occurs remains to be seen. But the loss of all these open access nights will definitely be a shock to the system.

UT: Do you see the new report as being overly pessimistic or do you think it’s spot on of what’s actually going to be taking place in astronomy next few years, such as in one scenario which described that only 50% of projected funding will be available?

Silva: I have no opinion on that. That was a boundary condition that the report used, and if I could predict that I would be in a different industry!

UT: Do you see any potential silver lining here, that this kind of tight funding could streamline things, or could help in the “persistent mismatch between the production rate of Ph.D.s and the number of tenure-track faculty or long-term astronomy positions” that the report talked about?

Silva: No. I think the higher-level issue is that astronomy in the last 20 years has been a field where the number of people who are professional astronomers has grown in this country because of a fortuitous funding cycle from all three of the major funding agents, NASA, NSF and the Department of Energy. But we are now in a downward cycle in funding for astronomy at the federal level and there is going to be a squeeze now. I think that one of the choices we’re going face as there is this squeeze and people begin to leave the field, how do we make sure that the those who are still in the field — especially our younger colleagues – that they are given the mentoring and nurturing and support they need to have vital careers.

But there’s a growing mismatch between the numbers of people who want funding and the funding that is available, there’s no two ways about it.

UT: Any final thoughts or things that you think are people I’m important for people to know about?

Silva: One of the opportunities that it creates on Kitt Peak is the ability to continue to move forward on our BigBOSS collaboration, which is a proposal to put a 5,000 target, multi-object spectrograph on the 4-meter Mayall telescope at Kitt Peak National Observatory, which allows you to do a large dark energy characterization experiment. The instrument is also exceptionally powerful for doing a variety of other investigations like galactic archaeology to map out kinematics in the galaxy, the chemical composition and the motions of galaxies and stars, and other very large data projects like that.

This report was actually quite supportive of that project moving forward. So even though reports recommend the NSF divest funding in the Mayall Telescope as an open-access telescope, it suggests there are ways forward to convert it from an open access platform to a survey facility. And that’s, I think, a silver lining in this. It doesn’t solve that cultural issue, but it was does mean we can continue to do high impact science with that instrument.

But I do see this as a big cultural change. A key question perhaps is, does the US have strong national observatory or not? And this report is leaning in the direction of not.

You can read an initial statement from NRAO (National Radio Astronomy Observatory) and AURA (Association of Universities for Research in Astronomy) on the AST report here, and another following statement from AURA here.

New Planet Kepler-21b Confirmed From Both Space And Ground

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Are you ready to add another planet to the growing list of discoveries? Thanks to work done by Steve Howell of the NASA Ames Research Center and his research team, the Kepler Mission has scored another. Cataloged as 21-b, this “new” planet measures about one and half times the Earth’s radius and no more than 10 times the mass… but its “year” is only 2.8 days long!

With such a speedy orbit around its parent star, this little planet quickly drew attention to itself. Kepler 21-b’s sun is much like our own and one of the brightest in the Kepler field. Given its unique set of circumstances, it required a team of over 65 astronomers (that included David Silva, Ken Mighell and Mark Everett of NOAO) and cooperation with several ground-based telescopes including the 4 meter Mayall telescope and the WIYN telescope at Kitt Peak National Observatory to confirm its existence.

At this point, observations place this hot little planet at about 6 million kilometers away from the parent star, where it has estimated temperatures of about 1900 K, or 2960 F. While this isn’t even anywhere near a life-supporting type of planet, Kepler 21-b remains of interest because of its size. The parent star, HD 179070, is just slightly larger than the Sun and about half its age. Regardless, it can still be seen with optical aid and it is only about 352 light years away from Earth.

Kepler light curve of HD 179070 showing the eclipse of Kepler-21b. The data cover 15 months. The figure shows the binned, and phase folded-data based on 164 individual transits over-plotted by the model fit (red line).

Why are findings like these exciting? Probably because a large amount of stars show short period brightness oscillations – which means it’s difficult to detect a planetary passage from a normal light curve. In this case, it took 15 long months to build up enough information – including spectroscopic and imaging data from a number of ground based telescopes – to make a confident call on the planet’s presence.

It ain’t easy being a little planet… But they can be found!

Original Story Source: NOAO News Release.

Student Aids In Tracking Down Near Earth Asteroids

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It’s one of the scariest scenarios that could face Earth. Can you imagine an asteroid impact? Even if it were a small event, it could have some far-reaching implications for life of all types here on terra firma. Knowing where and what we might be facing has been of constant concern, but one of the biggest problems is that there isn’t enough “eyes on the skies” to go around. There’s always a possibility that a flying space rock could slip through the proverbial cracks and devastate our planet. But, no worries… We’ve got a student to put to the test!

While most asteroids belong to the Jupiter-orbit class and pose absolutely no danger to Earth, there are exceptions to every rule. Known as Near Earth Objects (NEO), these orbiting stones also share our orbit – and our paths could cross. However, the juxtaposition is that we need to uncover as many of these stragglers as we can, document and track them for the most accurate information possible. Why? We need precise orbital information… A “somewhere in the neighborhood” just won’t do. By knowing exactly what’s out there, we stand a true chance of being able to deflect a problem before it arises. Right now a program headed by Mark Trueblood with Robert Crawford (Rincon Ranch Observatory) and Larry Lebofsky (Planetary Science Institute) is being executed at the National Optical Astronomy Observatory to help catalog NEOs – and it’s being assisted by a Beloit College student, Morgan Rehnberg, who developed a computer program called PhAst (for Photometry and Astrometry) that’s available over the Internet.

Because asteroids have a speedy window of observing opportunity, there can be no delays in reporting and tracking data. Time is of the element. While most astronomy targets are of long term imaging, asteroids require multiple digital images which are viewed via the “blink” method – similar to an old nickelodeon movie. At the same time, the coordinates for the NEO must be perfected and then computed. Right ascension and declination must be absolutely spot on. While there are computer programs currently able to do just that, none of them did exactly what’s required to stake the life of planet Earth on. Even though a better software program was required, there simply wasn’t enough time for the group to write it – but Trueblood saw it as the perfect opportunity for a summer student.

Many of us are familiar with the Research Experience for Undergraduates (REU) program, supported by the National Science Foundation and part of the National Optical Astronomy Observatory (NOAO). Not only has the REU made some fine imaging contributions, but they’ve learned what having a career in astronomy is really like and gone on to become professionals themselves. Enter Morgan Rehnberg, who just happened to have the right computer skills needed to tweak the current image viewer program (ATV, written in the code IDL) . Now you have a recipe for checking out as many images as needed in any order, and perform the astrometric (positional) as well as photometric (brightness) analyses.

While Morgan initially put his new software to use on existing image data, the first test happened this October during an observing session using the 2.1m telescope at Kitt Peak National Observatory. It was definitely a yellow alert when the group happened across a Potentially Hazardous Asteroid (PHA) designated as NEO2008 QT3. This wasn’t just a close rock… this was a rock that was going to pass within 50,000 km of Earth! Thanks to Morgan’s software upgrades, the team was able to correctly compute the brightness and distance of the PHA with 50% of the error margin gone. The resulting positional information was then submitted to the Minor Planet Center and accepted.

It’s a good thing they did it… PhAst!

Original Story Source: NOAO News. The computer program PhAST is available at http://www.noao.edu/news/2011/pr1107.php. In addition to the multi-object support, it contains the ability to calibrate images, perform astrometry (using the existing open source packages SExtractor, SCAMP, and missFITS), and construct the reports for the Minor Planet Center.