Third Closest Star to the Sun is Not A Star At All

The third closest star system has recently been found and it turns out to be a pair of faint "brown dwarfs" -- failed stars that just don't have what it takes to be a full-fledged sun. The new system -- known as Luhman 16, after its discoverer -- is 6.6 light years away. This means that light traveling from there to us would take a bit more than six and a half years to cross the distance between us. (The nearest star system is about 4.4 light years away, and the second nearest is 6 light years from us.)

I heard about this system from Dr. Gibor Basri, one of the discoverers of brown dwarfs, who gave a talk in the Silicon Valley Astronomy Lecture Series, which I have the privilege of organizing and moderating. Brown dwarfs were first named as part of her thesis by Jill Tarter, now the leading scientist searching for signs of extra-terrestrial intelligence, but then a graduate student getting her PhD at Berkeley. They are globes of hot gas that just don't have enough material to sustain the vast release of nuclear energy which powers ordinary stars.

It's the same in space as in Hollywood -- not everyone has what it takes to be a star. Just as many actors with ambitions to be in the movies wind up waiting on tables in Los Angeles, not every ball of hot material in space gets to be an on-going star. Some just glow briefly, especially with heat-rays (infra-red), but then slowly fade away. In fact, it was with the WISE infra-red telescope that astronomer Kevin Luhman discovered the brown dwarf system which now joins our list of intimate neighbors in space. (Its other name is WISE 1049-5319, which is a code that tells astronomers its location in the sky.)

In the picture with this article, you can see a later image of the system, taken with the giant Gemini telescope in Chile, that allowed astronomers to see that there were actually TWO brown dwarfs in the same star system, orbiting each other. We estimate they take about 25 years to go around. Interestingly, the Luhman 16 system is not only our third closest neighbor, but now appears to be the closest neighbor of our closest neighbor, the Alpha Centauri system. In other words, if you lived in the triple star system we call Alpha Centauri, and someone asked you, what's your closest neighbor in space, you would say Luhman 16. (Until recently, we thought WE were their closest neighbor, just like they were ours. But the brown dwarfs, which lie in the same rough direction as Alpha Centauri, but beyond them, now take our place as their closest neighbor.)

It's remarkable that something this close was just discovered. But that is a testament to how faint these failed stars really are. We are therefore able to find only the closer ones and many others that are further away remain undiscovered. The first brown dwarf was only found in 1995; today hundreds are known (thanks mostly to the WISE telescope.)

Dr. Basri's talk was videotaped and will eventually be up on our new YouTube Channel for the Silicon Valley Astronomy Lectures. You can go there now and see many other talks by noted astronomers: http://www.youtube.com/SVAstronomyLectures/

Weather on a Star

Astronomers using both the Hubble and the Spitzer space telescopes have gotten an indication of weather in the atmosphere of a kind of "failed star" called a brown dwarf. Stars are so far away that, in general, they look like points of light, even in our biggest telescopes -- so this is quite an achievement.

Brown dwarfs (a name coined by Jill Tarter, the scientist on whom Jodie Foster's character in the movie "Contact" was based) are large balls of hot gas that "ain't got what it takes" to be a star. They don't have the mass to continue making energy on their own, so after a brief period of glowing from how compressed they get at birth, they just fade away. (I like to compare them to all the actors that come to Hollywood with high hopes, maybe get a role as an extra in a TV show, but never make it to be real stars.)

This particular brown dwarf (which doesn't have a name, only a long catalog number) was observed not in visible light but in "infra-red" or heat rays, which allow us to see cooler glows. Both the Hubble and the Spitzer can detect and measure infra-red waves, but they "see" them from different depths in the atmosphere of the star. Daniel Apai, one of the astronomers doing the work, compared this to medical imaging, where different kinds of instruments can see different layers of your body.

As shown in the accompanying artist's interpretation (NOT a photograph!), there appear to be huge and deep clouds in the star's atmosphere, some of them as large as planet Earth! They move around in the atmosphere as the star spins every 90 minutes or so. They may somewhat resemble the largest regularly scheduled cloud we know in the solar system, the Great Red Spot of Jupiter (see the beautiful image below, from the Galileo spacecraft which orbited Jupiter.)

But the temperature in a brown dwarf is not cool like the atmosphere of Jupiter, so the clouds are likely to be made of different stuff from clouds on Earth and Jupiter. What might condense into clouds in a region which is 1100-1300 degrees Fahrenheit (600-700 degrees Celsius) in temperature? Mark Marley, another scientist on the team, suggests they are "composed of hot grains of sand, liquid drops of iron, and other exotic compounds."

Isn't it amazing that we can now do weather reports from a star?