Wolf 940′s Brown Dwarf Companion

by Paul Gilster on April 20, 2009

News about a nearby brown dwarf occupies us this morning, but first, a quick site update. The recent server problems did not, fortunately, result in the loss of any data, but I’ve had to make some temporary software changes to get Centauri Dreams back up. Expect more changes in coming weeks as I replace these fixes, so you may see things in transition for a time, but the server switchover is complete. One remaining problem is a snafu in image uploads that I hope to fix soon.

Now, to brown dwarfs. Seeing them is tricky business. Too small to be stars (although they do fuse deuterium), too massive to be planets, they’re hard to pick out in visible light and are generally detected at infrared wavelengths. Now a faint brown dwarf orbiting the nearby star Wolf 940 has been discovered. The primary is a red dwarf some 40 light years from Earth, orbited by its dim neighbor at a distance of some 440 AU.

This may bring to mind our recent discussion of Lorenzo Iorio’s work, which settled on a figure of 3,736-3,817 AU from the Sun as the nearest distance an undetected brown dwarf could exist near us. Wolf 940 B is obviously in a much tighter relationship than that with its primary. And astronomers studying the object hope that it may prove useful in telling us about the age and composition of brown dwarfs.

Ben Burningham (University of Hertfordshire) notes the dwarf’s cool temperature (by stellar standards) of 300 degrees Celsius, and says that its proximity to the red dwarf may come in handy:

“What’s so exciting in this case, is that we can use what we know about the primary star to find out about the properties of the brown dwarf, and that makes it an extremely useful find. You can think of it as a Rosetta Stone for decrypting what the light from such cool objects is telling us.”

The UKIRT Infrared Deep Sky Survey, based on Mauna Kea, is carrying out the work that resulted in this detection, flagging the brown dwarf as a companion to Wolf 940 after studying their common motion. We’re in an era of large scale surveys, and the question that now arises is whether brown dwarf/red dwarf binaries are unusual or whether we’re going to learn that red dwarfs often have such companions. In any case, Wolf 940 B should be helpful in finding out more about brown dwarfs and the nature of warm planetary atmospheres. The paper will run soon in Monthly Notices of the Royal Astronomical Society.

Speaking of nearby objects, Max Wolf, who discovered Wolf 940 some ninety years ago, seems to have had a penchant for finding them. He’s also the discoverer of Wolf 359, located 7.7 light years away and, like Wolf 940, a red dwarf (one with a relatively high flare rate, at that). Max Wolf was also a prolific asteroid finder, a pioneer in astrophotographic techniques, and the discoverer of several comets. He is not, however, associated with the so-called Wolf-Rayet stars. That would be the French astronomer Charles Wolf.

{ 12 comments }

Adam April 20, 2009 at 16:44

Hi Paul

An interesting paper on the arXiv discusses universes with different coupling constants for the nuclear force. Slightly stronger and it was believed that too many diprotons and dineutrons would form, using up all the hydrogen. Interestingly those two then decay into deuterium.

As the paper discusses some hydrogen remains over a broad range of coupling constants because it gets reproduced via photodissociation of the diprotons etc. So the situation isn’t as dire for life in such universes as previously believed. But the idea of more deuterium is not a bad thing either since most of the Sun’s energy comes from the D-D part of the protons->helium fusion cycle. The primary p-p reaction doesn’t produce much energy, but is vital for supplying deuterium to then react. In a Universe with more deuterium brown dwarfs would be longer-lived deuterium stars, lasting perhaps billions of years.

Administrator April 20, 2009 at 18:21

Interesting! Thus brown dwarfs nudge into stellar respectability in a universe with more deuterium. Do you have the arXiv reference?

Adam April 21, 2009 at 0:20

Hi Paul

That reference is at…

http://arxiv.org/abs/0904.1807

Big Bang Nucleosynthesis: The Strong Force meets the Weak Anthropic Principle

…I got the heads-up from the physics arXiv blog…

http://www.technologyreview.com/blog/arxiv/

…worth adding to the CD link list.

Phil Tynan April 21, 2009 at 8:47

Hello Paul,
The reference is listed at the bottom of the exerpt that follows my e-mail. A fascinating piece of work…almost makes me want to re-read Asimov’s ‘The Gods Themselves’ – except that the life in such an ‘ultrastrong-force’ universe could still be based on conventional chemistry. That much more deuterium coupled with a more vigorous strong-force interaction would markedly accelerate stellar evolution, wouldn’t it? So we’d end up with a universe composed of relatively high metallicity brown dwarves burning deuterium for billions of years as the favoured life sites and a slew of short-lived more massive stars, regularly undergoing supernova reactions and enriching the interstellar medium. Couple the following article with some of the recent speculations about a ‘Weakless Universe’ and maybe the Strong Anthropic Principle can be thrown out?

Regards,
Phil Tynan
PS – am a great fan of Centauri Dreams!

REFERENCE
Universe May Not Be “Fine-Tuned” for Life
The chemistry of life may be more robust than we thought against changes in the fundamental laws of physics.
Wednesday, April 15, 2009

The anthropic principle is the idea that the physical laws that govern our Universe are precisely those that allow complex life like ours to emerge. Many scientists have wondered at the balance of these laws, arguing that any small change would alter the universe so radically that life would be impossible. Why is the Universe so finely tuned for life, they ask.

Nobody has come up with a reasonable answer to this question but today James MacDonald and Dermott Mullan at the University of Delaware argue that matters may be more robust than we thought.

Their argument is about the strong nuclear force. Various physicists have noted that if the strong force were just a little stronger, then protons would bind together more readily. That would mean that soon after the Big Bang, most protons would join together to form diprotons, leaving few if any single protons available to form hydrogen. Consequently, chemistry as we know it would be impossible.

But this reasoning fails to take other factors into account, say MacDonald and Mullan. The biggest factor is that protons and neutrons will always bind more strongly than protons and protons, regardless of the strength of the strong force. So although diprotons would form in this universe, they would also tend to decay into deuterons.

So hydrogen (and deuterium) chemistry would be just as likely in a Universe in which the strong force were stronger. (Of course, how the change would affect the the nucleosynthesis of other elements is another question.)

The work gives the lie to some of the more extraordinary claims regarding the anthropic principle. For example, some argue that since we are unable to find anything special about the combination of laws in our Universe, then maybe any permutation is possible. And if any permutation is possible, then perhaps these combinations exist in countless other universes. Of course, the only one we would experience is the one in which the laws are fine-tuned for our existence.

That’s an extraordinary line of argument. But the alternative–that organic chemistry is an emergent property of a wide range of the parameters governing the basic laws of physics–is even more jaw dropping.

MacDonald and Mullan’s work gives a tantalising hint that this idea might be worth pursuing a little more diligently.

Ref: arxiv.org/abs/0904.1807: Big Bang Nucleosynthesis: The Strong Force meets the Weak Anthropic Principle

Adam April 21, 2009 at 9:06

Speaking of small exoplanetary objects…

A 1.9 Earth mass exoplanet (period 3 days)
has been detected around Gliese 581 (Mayor et al).
See
http://exoplanet.eu/planet.php?p1=Gl+581&p2=d

It is the lightest planet detected up to date around a main sequence star.

In addition, the planet Gliese 581 d has a revised period of 67 days,
bringing it in the habitable zone of the parent star.

Jean Schneider

…email alert from the Exoplanet Encyclopedia

Administrator April 21, 2009 at 9:33

Phil Tynan writes:

So we’d end up with a universe composed of relatively high metallicity brown dwarves burning deuterium for billions of years as the favoured life sites and a slew of short-lived more massive stars, regularly undergoing supernova reactions and enriching the interstellar medium. Couple the following article with some of the recent speculations about a ‘Weakless Universe’ and maybe the Strong Anthropic Principle can be thrown out?

Fascinating! I appreciate the arXiv reference re the anthropic principle and will give it a look. And heck, why not re-read the Asimov? Always provocative.

Doowop April 21, 2009 at 16:47

Brown dwarfs may account for the universe’s missing mass, the dark matter needed to explain the gravitational models of the universe’s expansion. Since 90% of the universe’s mass is unseen, there may be vastly more brown dwarfs than stars:

“What if space is littered with these failed stars, scattered between the bright ones like a stellar Polynesia, making interstellar travel a series of short hops, rather than a single gigantic one? What if a simple fusion reactor carried just enough fuel to push a spacecraft to our solar system’s Planet X in reasonable time? What if it could refuel there, harvesting just enough hydrogen or deuterium or helium to limp along to another dark neighbor, and another, and another? Granted, it would take a long, long time to get to Alpha Centauri that way, and probably a much, much longer time to find a planet somewhere that looked even remotely like our rain- and sun-drenched Earth. But given the likelihood of tidally warmed moons, and the obvious possibilities for life there, we may just find that the cold, dark spaces are where most of the action is anyway.”

Instead of just being convenient refueling stations for voyages to other solar systems, brown dwarfs could be the hubs of mini-solar systems of their own. The first picture of an extrasolar planet is of a planet orbiting a brown dwarf. While brown dwarfs give off little in the way of light, they do generate heat. Enough heat to make life possible on the planets orbiting them:

“Discs around brown dwarfs typically weigh about one-tenth of the mass of the star itself, so in this case it probably contains one or two Jupiter masses of available planet-building material. “I’d speculate that it could build a Saturn, or maybe a few smaller Earth-sized planets,” says Luhman. What is more, these would-be planets could be habitable. The surface temperature of the mini brown dwarf is about 2000°C, which means that any planet 1.5 to 7 million kilometres away could maintain liquid water. The disc probably straddles this range. Luhman hopes to find out whether even smaller objects – perhaps as little as five times the mass of Jupiter – can reign at the centre of nascent planetary systems. “It’s still an open question as to how small you can go, but hopefully we’ll be able to answer that soon.”

There may be dozens or hundreds of mini-solar systems between Sol and Alpha Centauri. With the discovery of brown dwarfs, free floating planets between the stars, and extrasolar planetoids like Sedna, future space explorers may find plenty to keep them occupied in our own solar neighborhood for centuries to come. While not the galaxy spanning empires and federations of science fiction, it would be enough for our species to explore far into the future without the need for exotic starflight technologies – a galactic version of “the universe in a grain of sand.”

As for life on world orbiting brown drawfs, visible light may not be necessary. There are certain organisms for example that use infrared here on Earth for photosynthesis:

“Yet other organisms, such as the purple and green bacteria (which, by the way, look fairly brown under many growth conditions), contain bacteriochlorophyll that absorbs in the infrared, in addition to in the blue part of the spectrum. These bacteria do not evolve oxygen, but perform photosynthesis under anaerobic (oxygen-less) conditions. These bacteria efficiently use infrared light for photosynthesis. Infrared is light with wavelengths above 700 nm that cannot be seen by the human eye; some bacterial species can use infrared light with wavelengths of up to 1000 nm.”

Absent competition from other forms of photosynthesis, there probably isn’t any major obstacles to life derived from infrared instead of the visible spectrum.

Ronald April 22, 2009 at 9:31

@Doowop:
what I understood from databases, such as Nstars, as well as from a few astronomers, is that star abundance increases exponentially with decreasing stellar mass, but drops off sharply below a certain mass (arounf 0.2 solar mass, if I am not mistaken).

This could partly be attributed to observational bias, the smallest stars being hardest to detect. But not entirely, because it also holds true in our galactic neigborhood.

It is not unlikely that there exists an optimum mass for stellar aggregation, above ánd below which abundance decreases.

In that case brown dwarfs may still be rather common, but not the most common.

I still remain a solartype chauvinist ;-)

Administrator April 22, 2009 at 15:22

Doowop writes:

Brown dwarfs may account for the universe’s missing mass, the dark matter needed to explain the gravitational models of the universe’s expansion. Since 90% of the universe’s mass is unseen, there may be vastly more brown dwarfs than stars:

Fascinating post, Doowop, and it got me looking back at the observational attempts to distinguish between MACHOs (large dark matter candidates like brown dwarfs, etc.) and WIMPs (exotic particle solutions). That resulted in today’s post, which reports on the findings thus far, but as I note at the end, we’re a long way from closing the book on the nature of dark matter!

spaceman April 28, 2009 at 0:35

Hi folks,

It seems to me as if every couple of years astronomers reestimate how many brown dwarfs exist in the Milky Way. Why is this? It goes from, “there are as many of these as there are small stars” to “brown dwarfs are not as common as MS stars. ” Which is it? Has Spitzer weighed in on this?

Tobias Holbrook May 5, 2009 at 10:00

We’ll just have to wait for WISE to answer the question. Hopefully it’ll find a few L-types withing several lighmonths, and maybe some Y-types within a few light days.

ljk June 23, 2009 at 13:07

A Massive Substellar Companion to the Massive Giant HD 119445

Authors: Masashi Omiya, Hideyuki Izumiura, Inwoo Han, Byeong-Cheol Lee, Bun’ei Sato, Eiji Kambe, Kang-Min Kim, Tae Seog Yoon, Michitoshi Yoshida, Seiji Masuda, Eri Toyota, Seitaro Urakawa, Masahide Takada-Hidai

(Submitted on 20 Jun 2009)

Abstract: We detected a brown dwarf-mass companion around the intermediate-mass giant star HD 119445 (G6III) using the Doppler technique. This discovery is the first result from a Korean-Japanese planet search program based on precise radial velocity measurements. The radial velocity of this star exhibits a periodic Keplerian variation with a period, semi-amplitude and eccentricity of 410.2 days, 413.5 m/s and 0.082, respectively.

Adopting a stellar mass of 3.9 M_solar, we were able to confirm the presence of a massive substellar companion with a semimajor axis of 1.71 AU and a minimum mass of 37.6 M_Jup, which falls in the middle of the brown dwarf-mass region.

This substellar companion is the most massive ever discovered within 3 AU of a central intermediate-mass star. The host star also ranks among the most massive stars with substellar companions ever detected by the Doppler technique.

This result supports the current view of substellar systems that more massive substellar companions tend to exist around more massive stars, and may further constrain substellar system formation mechanisms.

Comments: 17 pages, 5 figures, PASJ accepted

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Cite as: arXiv:0906.3762v1 [astro-ph.EP]

Submission history

From: Masashi Omiya [view email]

[v1] Sat, 20 Jun 2009 00:09:02 GMT (81kb)

http://arxiv.org/abs/0906.3762

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