Luhman’s Latest: A New, Nearby Brown Dwarf

by Paul Gilster on April 29, 2014

Kevin Luhman (Pennsylvania State University) has focused much of his research on the formation of low-mass stars and brown dwarfs in star-forming regions near the Sun. This involves working with relatively young stars, but Luhman is also on the alert for older objects, very cool brown dwarfs in the solar neighborhood. Brown dwarfs cool over time, and as Luhman describes on his university web page, they are ‘valuable laboratories for studying planetary atmospheres.’ They also give us a chance to test theories of planet formation in extreme environments.

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Now we have Luhman’s latest, and it would not be a surprise if the whole category of nearby, cool stellar objects begins to get referred to as ‘Luhman objects’ or some such. Remember that it was just back in March that the astronomer discovered, using WISE images, a binary brown dwarf system at a scant 6.5 light years from Earth. The new find is WISE J085510.83-071442.5. It has the third highest proper motion and the fourth largest parallax of any known star or brown dwarf, and can lay claim to being, at least for a time, the coldest brown dwarf on record.

Image: Penn State’s Kevin Luhman, a specialist in low mass stars and brown dwarfs, who is filling in our map of such objects close to the Sun.

How cold? This object is thought to be between -48 to -13 degrees Celsius, colder than previous record holders, which were found to be close to room temperature. WISE imagery from 2010 was confirmed by two additional images taken by Spitzer in 2013 and 2014, with further observations at the Gemini South telescope on Cerro Pachon in Chile. The WISE and Spitzer data were used to measure the distance to the object via parallax. It turns out to be 7.2 light years away, fitting nicely into the chart below, which shows the Sun’s immediate neighborhood.

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Image: This diagram illustrates the locations of the star systems closest to the sun. The year when the distance to each system was determined is listed after the system’s name. NASA’s Wide-field Infrared Survey Explorer, or WISE, found two of the four closest systems: the binary brown dwarf WISE 1049-5319 and the brown dwarf WISE J085510.83-071442.5. NASA’s Spitzer Space Telescope helped pin down the location of the latter object. The closest system to the sun is a trio of stars that consists of Alpha Centauri, a close companion to it and the more distant companion Proxima Centauri. Credit: NASA/Penn State University.

That’s a fascinating chart, and while all of us can share the determination to learn more about brown dwarf and planet formation and the atmospheres of cold objects, some of us also think in terms of targets for future probes, hoping that brown dwarf hunter Luhman may turn up something even closer than the three he has already discovered. Objects as cool as Luhman’s latest can all but disappear at visible wavelengths, but their infrared glow makes detection possible, with surely more to come. Thus Michael Werner, a Spitzer project scientist at JPL:

“It is remarkable that even after many decades of studying the sky, we still do not have a complete inventory of the sun’s nearest neighbors. This exciting new result demonstrates the power of exploring the universe using new tools, such as the infrared eyes of WISE and Spitzer.”

We’re talking about an object somewhere between 3 and 10 times the mass of Jupiter, which makes WISE J085510.83-071442.5 one of the least massive brown dwarfs known, if indeed it is a brown dwarf rather than a free-floating gas giant that has been expelled from some undetermined star system. Luhman comments on the latter possibility in the paper on this work:

At this mass, WISE 0855−0714 could be either a brown dwarf or a gas giant planet that was ejected from its system. The former seems more likely given that the frequency of planetary-mass brown dwarfs is non-negligible while the frequency of ejected planets is unknown. Assuming that WISE 0855−0714 is a Y dwarf, the four closest known systems now consist of two M dwarfs and one member of every other spectral type from G through Y.

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Image: This artist’s conception shows the object named WISE J085510.83-071442.5, the coldest known brown dwarf. Brown dwarfs are dim star-like bodies that lack the mass to burn nuclear fuel as stars do. WISE J085510.83-071442.5 is as cold as the North Pole (or between minus 48 to minus 13 degrees Celsius). The color of the brown dwarf in this image is arbitrary; it would have different colors when viewed in different wavelength ranges. Credit: NASA/JPL-Caltech/Penn State University.

The paper goes on to note that the newly discovered brown dwarf now offers the chance to test various atmospheric models in an unexplored temperature regime, something that will require refining the parallax measurement and ‘deeper near-IR photometry to better constrain its spectral energy distribution.’ We’ll also need to take advantage of near-term advances in our spectroscopy of the sort the James Webb Space Telescope should make available.

The paper is Luhman, “Discovery of a ~250 K Brown Dwarf at 2 pc from the Sun,” The Astrophysical Journal Letters Vol. 786, No. 2 (2014), L18 (abstract / preprint). A JPL news release is also available.

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{ 27 comments… read them below or add one }

Harry R Ray April 29, 2014 at 9:24

Well, there goes the exomoon candidate! Death by reclassification! If you have to PROOVE that a 4Mj object has been EJECTED from a planetary system for it to be a planet, then MOA-BLG 252 is either a 0.5Me PLANET or a 19Me planet! If these objects ARE stsrs, they should ALSO be reclassified as what Alan Boss calls “sub brown dwarves, because they are not massive enough to have EVER undergone ANY KIND of fusion reactions! Also, just as a point of interest, by coincedence only, The temperature at the cloud tops of this new brown dwarf is almost EXACTLY the estimated surface temperature of Kepler 186f.

graywyvern April 29, 2014 at 12:47

this object badly needs a better name!

I think the twin brown dwarfs could be “Romulus” & “Remus”…then “Rhea Silvia” (the mother) or “Luperca” (the name of the wolf) suggest themselves.

m.

andy April 29, 2014 at 13:33

Now we have Luhman’s latest, and it would not be a surprise if the whole category of nearby, cool stellar objects begins to get referred to as ‘Luhman objects’ or some such.

Bear in mind, however, that this object will probably not be known as Luhman 17 (or whatever)… the Luhman 16 designation for WISE J104915.57–531906.1 is a binary star “discoverer designation”. So probably may take a while longer for this object to get a more memorable designation, unless of course Kevin Luhman discovers that it too is a binary.

Alex Tolley April 29, 2014 at 13:40

Does the temperature mean that we could theoretically inhabit such a body, in fusion powered floating cities? The living volume within a reasonable temperature and pressure regime would be immense. If there is any methane, there would be carbon for life and structural elements. Other life requiring elements and metals might need to be acquired from elsewhere which may be a potential problem. Given the distance, possibly reachable in a human [extended?] lifetime.

Michael April 29, 2014 at 14:38

I am getting around 200 km/s transverse velocity, so at around 5Gyr of age it could have travelled of few millions of lyr. Due to its temperature it is unlikely to have gone through a fusion or intense tidal heating stage or it could just be very old. Most likely to me anyway is it is a stellar free forming planet rather than a ‘flanet’ (flung out planet) that is very old. I can’t wait until they find one closer.

Daniel April 29, 2014 at 15:28

“But scientists estimate it is probably a brown dwarf rather than a planet since brown dwarfs are known to be fairly common.”

Scientist said that is more likely to a Brown Dwarf that a Planet,I don’t know what is the scientific base they use to state it,because far as I know brown Dwarf are less common than stars,but from microlensing estimates Rogue Planet are fairly common Object ever more common that Brown Dwarfs,they are just too cold to be detect

well this is far as I know.

Adam April 29, 2014 at 15:56

Being a cool brown dwarf the object would be about Jupiter size thus its surface gravity would be a multiple of Jupiter’s – at 10 Jupiter masses that’s about 25 gee. So not a colonisation prospect by itself. Of course it might have moons/planets and they might be warm enough via tidal heating, if suitably wrapped in insulating ice. More speculatively the planets might have attracted thick hydrogen blankets to warm their surfaces – Earth and Mars probably did so aeons ago.

Danangel April 29, 2014 at 17:30

Alex Tolley, why would anyone want to live there, when there are so many warm stars around? I just don’t see the point.

Norman Wells April 30, 2014 at 4:28

@Danangel l agree with your comments .For those of us interested primarily in the search for intelligent extra terrestrial life the examination of the various discovered bodies needs to become more focused on a search for potential candidates with a similarity to our own planet. Even if widely divergent life forms exist we are unlikely to be able to communicate with them , and much less able to exist in their environment. Personally I am inclined to think that if any other intelligent life forms exist they will closely ressemble human beings

kzb April 30, 2014 at 8:07

As someone not in this area of expertise, I look at the images at the end of the paper and realise how difficult it must be to identify and confirm these very faint objects. It was found initially by proper motion on the WISE images, but multiple (expensive) instruments had to be employed to confirm its nature.

This one person, Kevin Luhman, has found the third and fourth nearest systems in the last few months. Given all these factors surely there must be a lot more similar objects still awaiting discovery in our locality.

I also note that 3 out of the 7 nearest objects are brown dwarfs, that’s 43%.

Alex Tolley April 30, 2014 at 10:42

Adam puts the stake in the heart of outposts or colonies in the atmosphere. I wasn’t thinking of the g limitations of such a body.

@Danangel – People live in all sorts of places, most of which I personally wouldn’t even think of as even “habitable”. Life, including humans, will tend to fill all possible niches.

Alex Tolley April 30, 2014 at 10:49

@Norman Wells

I am inclined to think that if any other intelligent life forms exist they will closely ressemble human beings

That is extremely unlikely given how evolution works. Our vertebrate body plan alone was a chance event (compare it to the other major phyla on Earth) and to expect that our human form would evolve on top of this on another world is extremely unlikely. Just having an alien that could think enough like us to communicate might be rarer than we think.

Curt Wohleber April 30, 2014 at 11:21

“The color of the brown dwarf in this image is arbitrary; it would have different colors when viewed in different wavelength ranges.”

What color would it be if I were looking through a porthole on my space yacht?

andy April 30, 2014 at 16:49

@Daniel: regarding the microlensing results, there are various questions surrounding that estimate, and in any case there is the same ambiguity between free-floating planets and (sub-)brown dwarfs there too. Rogue planets happens to sound better for a press release ;-)

It is possible for example that several of those are planets on sufficiently wide orbits (~10–30 AU) that the star was not detectable in the light curve, see Quanz et al. (2012) for discussion of this. It’s also worth noting that the claim of the high incidence of free-floating planets is substantially at odds with the observations of young clusters, see for example the Scholz et al. (2012) study of NGC 1333.

Phil April 30, 2014 at 19:34

“What color would it be if I were looking through a porthole on my space yacht?”

Assuming you were using your own unaided eyes, it would be a totally dark disk against the glow of the Milky Way. Unlike the Luhman 16 BDs, which are hot enough to radiate in the visible, at 250k, this world not going to radiate in the visible at all, and there’s no nearby star to illuminate it.

I’d like to think there might be a powerful lightning show though! Even with a presumably powerful magnitic field, there would be no stellar magnetic field to interact with – would there be aurorae? I guess not?

P

Flem May 1, 2014 at 0:57

@Curt Wohleber

I would estimate there would be too little light out there to make out any color at all, so probably dark, and grey, like the night side of solar system objects. That however wouldn’t make a very good picture for publication.

kzb May 1, 2014 at 8:05

Planetary system formation models show apparently show many planets are ejected. But on average it is the smaller planets that get ejected, and the big planets that do the ejecting. This new object is towards the top end of planet masses so surely its origin as an ejected planet is statistically unlikely. This makes me favour the ‘sub-brown dwarf’ description over the ‘rogue planet’ (and related terms) description.

On the other hand, one out of seven of the nearest objects is apparently a planetary mass object. This is way higher frequency than Scholz et al (Andy’s post above) and other similar studies. This could be a fluke of course, but I would argue this is likely to be the first one out of many that exist locally. So I wonder if there is a tension between the cluster frequency and the observed frequency, or there will be in the future ?

Lionel May 1, 2014 at 10:38

@ kzb

I wouldn’t dismiss this being an ejected object – smallness is all relative – consider a double or triple star system or a star cluster – from this point of view this ‘sub-brown dwarf’ or ‘rogue super jupiter’ can be a small ejectable object

Lionel May 1, 2014 at 10:54

As for people living in all sorts of places, last year I was studying with a fellow from Magadan in the far east of Russia – it’s a mining town about 2700 kilometers north-north-east from Tokyo

If I remember correctly he said Magadan’s winter lasts for about 10 months of the year, with spring and autumn lasting less than a month and a 2 week summer. The worst time of the year, surprisingly, is summer – with temperatures of 45 degrees C and clouds of mosquitoes everywhere. Elementary schools kids are allowed to stay at home when temperatures drops below minus 45 degrees C – unfortunately most of the time it hovers around minus 42, he told me. “But it was ok, because as a young kids you don’t feel the cold”

Of course since long before the Russians came to those lands, many fascinating tribal peoples lived in the world’s Arctic regions for thousands of years, as well as Tibetan people living in similarly harsh conditions in the remotest parts of the Himalayas.

Michael May 1, 2014 at 13:13

@Phil April 30, 2014 at 19:34

‘I’d like to think there might be a powerful lightning show though! Even with a presumably powerful magnitic field, there would be no stellar magnetic field to interact with – would there be aurorae? I guess not?’

Around Jupiter Io’s material is expelled and is accelerated in its magnetic field, the same could happen around this world if a near in moon is tidally heated to a high temperature, it only takes a few ions to start the cascade process.

kzb May 1, 2014 at 13:40

Lionel, yes I am sure you are right, but the papers I read on planetary system formation and planet ejection didn’t seem to consider the binary/triple star cases. Being in a birth cluster is very much part of the model, and close stellar encounters in the cluster result in planets being stolen, ejected, or put into inclined and elliptical orbits (like Sedna).

Now you mention it, perhaps this is the reason why there might be a greater frequency of PMOs observed than are seen in these star forming regions.

Ricardo Orsini (ROCA) May 1, 2014 at 20:01

As it is 3-10 Jupiter´s masses, it seems to be a rogue planet as 13MJ is the lower limit current known for brown dwarfs mass.

kzb May 6, 2014 at 7:54

Ricardo, 13MJ is the lower limit for deuterium fusion. So I would agree with the term PMO (Planetary Mass Object). The term Rogue Planet implies it has escaped from a planetary system (to me it does anyhow). But we don’t know if this is true in this case. What is known is that objects in this mass range form in molecular clouds, apparently by the same mechanism that produces proper stars. It’s a Y-class brown dwarf in Luhman’s paper.

Lionel May 10, 2014 at 11:25

@kzb

Is there a lower size limit to objects that can form within molecular clouds? Is there any thinking whether a Jupiter, Neptune, Earth or smaller sized object could form from a molecular cloud without a star being formed?

Been interested in this question for a while. I presume there is a lower limit but never seen any information on this, and didn’t find any answers through googling

kzb May 13, 2014 at 7:44

Lionel, I believe the lower limit is about one Jupiter mass. So anything much less than this forms as a planet (from a proto-planetary disk).

I suppose this is why there is a grey area between a Jupiter and low mass brown dwarfs, these could be formed by either mechanism.

ffp May 20, 2014 at 6:02

Luhman Hydrae. A discoverer constellation designation for WISE 0855–0714.

ljk June 11, 2014 at 12:51

The Smallest Star

By Phil Plait

Astronomers may have identified what may be the smallest known star. And not just the smallest known star but quite possibly the smallest possible star. If it were any smaller, it might not even be a star anymore.

The star in question is called 2MASS J05233822-1403022, but I’ll call it J0523 for short (the name comes from its discovery in the 2-Micron All Sky Survey (2MASS), together with its coordinates on the sky). As weaklings go, it’s just about the weakest: It shines only 1/8,000th as brightly as the Sun, has a temperature of 1,800° C (compared with the Sun’s 5,600°), and a diameter a mere 0.09 times the Sun’s—smaller than Jupiter!

Full article here:

http://www.slate.com/blogs/bad_astronomy/2014/06/11/the_brown_dwarf_limit_astronomers_have_found_the_smallest_star_known.html

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