WISE: New Stars and Brown Dwarfs

by Paul Gilster on March 10, 2014

Just how early we are in our thinking about traveling beyond the Solar System is revealed in a comment made by Ned Wright, principal investigator of the WISE mission. “We don’t know our own sun’s backyard as well as you might think,” said Wright. And he goes on to say, “We think there are even more stars out there left to find with WISE.” That’s a wake-up call indeed given how much WISE has already told us, and what two new studies have brought to light.

Davy Kirkpatrick (Caltech) led one of these, examining data from the Wide-field Infrared Survey Explorer mission that performed two full scans of the sky in 2010 and 2011, capturing images of almost three-quarters of a billion galaxies, stars and asteroids. Analyzing data using NASA’s AllWISE program, which makes it possible to compare the datasets more effectively, Kirkpatrick’s team found 3,525 new stars and brown dwarfs within 500 light years of the Sun.

These objects, says Kirkpatrick, were totally overlooked before now. In any case, the number of stars and brown dwarfs within range of conceivable future exploration is something we have to clarify, building a 3-D map of nearby space that goes beyond the long-identified bright targets like Alpha Centauri and Epsilon Eridani. We’re still learning how many brown dwarfs are out there, and trying to determine not only how they form but how frequently they form planets. Note this from the Kirkpatrick paper: “…both studies missed objects that the other found, demonstrating that many other nearby objects likely await discovery in the AllWISE data products.”

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Image: A nearby star stands out in red in this image from the Second Generation Digitized Sky Survey. The star, called WISEA J204027.30+695924.1, was initially discovered using data from NASA’s Wide-field Infrared Survey Explorer (WISE), which scanned the entire sky in infrared light in 2010 and early 2011, before ending its primary mission. Objects that are close to us will appear to move more than distant objects when viewed over time. By comparing images taken by WISE six months apart, astronomers are finding thousands of stars and brown dwarfs in our sun’s “backyard.” The star WISEA J204027.30+695924.1 is a dim star called an L-subdwarf, and is particularly fast moving most likely because it’s old. Older stars tend to have more time — billions of years — to get flung around, and pick up speed. Credit: DSS/NASA/JPL-Caltech.

Penn State’s Kevin Luhman led a second study of the WISE data, cataloging 762 objects (with some overlap with the Kirkpatrick trove). Luhman’s work is getting most of the press because it seems to put to rest the existence of an object many of us had rather hoped to find: Planet X. Call it what you will — Planet X, Nemesis, Tyche — the idea of a large, undiscovered body disrupting the outer Solar System has been around for a long time. Indeed, it was the search for such a body that led to Clyde Tombaugh’s discovery of Pluto back in 1930, although it soon became clear that Pluto wasn’t the much larger object Percival Lowell was hoping to find.

We learn from the Luhman paper that if an undiscovered planet is out there, it’s not a large one. This NASA news release tell us that Luhman’s team can rule out any object larger than Jupiter out to a distance of 26,000 AU, and any object of Saturn size or larger out to 10,000 AU. The interesting idea that a large planet or small star might periodically disrupt cometary orbits in the Oort Cloud takes a hit here, or at least we can say that the new work puts limits on how large such an object could be and how far from the Sun it might exist if part of our system.

Meanwhile, I still find it tremendously interesting that WISE is pulling up stars and brown dwarfs we knew nothing about before, and I’m reminded of the 2013 discovery of the nearby Luhman 16AB, otherwise known as WISE J104915.57-531906, a pair of brown dwarfs some 6.5 light years away. When WISE data revealed this binary, it uncovered the third closest system to the Sun, the closest to be discovered in almost a century. We’re already studying atmospheric features on Luhman 16B, which shows variations in brightness as it rotates. For more on this, see Focus on the Nearest Brown Dwarfs. A possible companion object is also being investigated.

The Kirkpatrick paper is “The AllWISE Motion Survey and The Quest for Cold Subdwarfs,” Astrophysical Journal, Vol. 783, No. 2 (2014), 122 (abstract / preprint). The Luhman paper is “A Search for a Distant Companion to the Sun with the Wide-field Infrared Survey Explorer,” Astrophysical Journal, Vol. 781, No. 1 (2013) (abstract).

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{ 10 comments… read them below or add one }

RobFlores March 10, 2014 at 11:40

Glad there was no Planet X.
There was also another extremely low probability event that has been eliminated.

Namely, rogue small brown dwarf inbound to our solar system at high speed.
A brown dwarf can be sent careening off into space due to primary running our fuel and subsequent supernova explosion.
If one of those had been moving fast toward us, we might not
see it until it is within a couple of dozen years from arrival. Even a glancing blow affecting the orbits of any of the Jovians by sending them on
elliptical orbits to the inner solar system would have the potential to create
chaotic climate for Earth to due to increase orbital eccentricity. Obcourse
such a jovian has the potential to send the Earth as snack for our Sun.

I wonder if WISE could spot small icy bodies being absorbed by an
inbound black hole?

Michael March 10, 2014 at 13:28

@RobFlores March 10, 2014 at 11:40

‘There was also another extremely low probability event that has been eliminated.’

Replaced by another extremely low probability event and I bet you if you add up all these improbable events it is highly probable we will be hit by something at sometime in the future.

‘Namely, rogue small brown dwarf inbound to our solar system at high speed.’

Mike March 10, 2014 at 14:51

To RobFlores, if we had a black hole approaching I would think the detection would more likely be done by high energy instruments eg. FERMI.
If said black hole is snacking on Ort cloud objects I think there would be a lot of X-ray and Gamma ray burping. And visible light emissions as well.

Not having a distant late M-dwarf or brown dwarf companion to Sol doesn’t surprise me as the WISE results have only supported previous though less comprehensive searches. As for rogue planets, I’m happy that we apparently don’t have anything really large, really close by moving inward really quickly.

Also I’m always pleased about a more accurate understanding of the Solar neighbourhood. What I would really like even more is a complete planetary census of all nearby stars out to 20 light-years or so while I’m still around to appreciate it. Call me selfish.

Peter Chapin March 10, 2014 at 20:15

Will Gaia be able to track some of these new dim objects that are now being discovered? I wonder if such objects have anything unusual going on with their trajectories through interstellar space. Their low mass might make detecting planetary wobbles relatively easy for an instrument like Gaia.

Isaac Arthur March 10, 2014 at 21:54

Huh, not that I’m a big fan of the Nemesis idea but isn’t the Planet-X/Nemesis hypothetical giant/star supposed to be out at 90,000 AU, not 26/10k AU? 26 million year orbit, Kepler says: T²=a³, 26,000,000²=> a= 87,764 AU? Am I missing something here or are they kind of jumping the gun?

josh March 11, 2014 at 1:20

The class of solar system objects ruled out in this analysis consisted of the less interesting ones IMO. Terrestrial planets comparable to the inner solar system bodies in Oort Cloud orbits would have far greater potential usefulness, tendency to promote outer Solar System exploration and astrobiological significance.

Adam March 11, 2014 at 5:00

Hi All
Does seem a shame there is no Tyche – as dubbed by Matese and Whitmire – since its gravitational influence neatly explained the comet distribution seen. Still a lot that *might* be between the stars – 100,000 Plutos and 1 trillion comets, per star, according to best estimates. If we can work out a clever way of using them all, that’s a lot of territory to homestead. The Sun puts out ~2 billion times more light than the Earth intercepts, and even the dimmest Main Sequence star puts out ~1/8,000th of that. Hundreds of thousands of “Earths” could be sustained by every Red dwarf. Really clever advanced civilizations would figure out how to light the swarms around the stars without building something as inelegant as a Dyson Sphere or similar sidereal engineering juggernauts.

kzb March 11, 2014 at 8:47

Does anyone know what per cent of the sky was surveyed for the outer planet search ?

I ask because the searches often leave out several degrees either side of the galactic disk plane.

Paul March 11, 2014 at 14:00

I wonder what the limits are for smaller planets, say ones of Earth or even Mars size. These might be too cold to show up well in WISE data.

The reason I ask is that such planets, if they exist, might be the best places to mine 3He in the solar system, assuming their exospheres are cold enough to have retained that isotope over the age of the solar system.

Michael March 11, 2014 at 14:57

‘This NASA news release tell us that Luhman’s team can rule out any object larger than Jupiter out to a distance of 26,000 AU, and any object of Saturn size or larger out to 10,000 AU…’

Any brown dwarf would be around the size of Jupiter but would emit a lot more infrared radiation, so the statement ‘any object larger than Jupiter out to a distance of 26,000 AU’ means little. Also the Oort cloud is ~50 000 Au away, a heavy massed object could also be on the outside of this cloud as previously mentioned and theorised as Nemesis.

@Adam March 11, 2014 at 5:00

‘Really clever advanced civilizations would figure out how to light the swarms around the stars without building something as inelegant as a Dyson Sphere or similar sidereal engineering juggernauts.’

Maybe we could build artificial stars by colliding beams of fuel to fusion velocities to create charged beams of energy that could be used to heat a sphere to incandescence for light and heat. These ‘artistars’ they could also be placed in a Lagrange point between two orbiting objects as a stable source of light/heat to heat both atmospheres/surfaces. The beams could be diverged and slowed magnetically and allowed to impact any atmosphere that is formed from the heating process releasing light and heat. A lot of energy would be required but could be reduced by adding greenhouse gases to the atmosphere to limit thermal escape.

Just thinking and dreaming out aloud…

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