Just last year, I posted the news that astronomer Kevin Luhman of Penn State had discovered the third closest star system to our own. It consisted of a pair of failed stars -- stars containing too little material to shine consistently with visible light and thus commonly called brown dwarfs.
Now Luhman has done it again. He recently announced the discovery of the fourth closest system -- this one consisting of the coldest brown dwarf ever found. Known only by a long catalog number giving its cosmic "latitude and longitude" (WISE J085510.83-071442.5), the wanna-be star is 7.2 light years away. That's right in our neighborhood as far as astronomical objects are concerned.
Our best estimate of its mass is that it weighs only as much as 3 to 10 Jupiters. So, really, it could be more of a free-floating planet rather than a brown dwarf. But since brown dwarfs are more common (planets are found more frequently around stars than by themselves), the discoverer is betting it's just a very cold and poorly endowed brown dwarf.
The image accompanying this note is just an artist's conception of what such a cold, failed star might look like. After observing it with a variety of space-based telescopes (such as WISE and Spitzer, which are sensitive to infra-red or heat rays and not light), Luhman and his colleagues estimate that the outer temperature of this strange neighbor is as cold as the Earth's North Pole. (Estimates vary from -54 to 9 degrees Fahrenheit, or -48 to 13 Centigrade.) So its outer layers are like those of the giant planets far from our Sun, and nothing like a real star. Stars have temperatures thousands of degrees hot.
What is remarkable to me is that, after 400 years of using telescopes, and more than 50 years of instruments in space, we are still discovering our closest neighbors! It's not our fault, of course -- this neighbor was very shy, not shining with the kind of rich light power that our closest neighbor, the triple star system Alpha Centauri, gives off. And in space, as on Earth, it's often the show-offs that get the attention.
I'll share a little secret with you. If you follow astronomy developments, you might have noticed that there are a lot of news stories that come out at the beginning of January. The reason is that the nation's professional astronomers have their big meeting each year in early January, and many universities and observatories save up their big announcements to coincide with a talk or paper being delivered at that meeting.
This year was no exception -- many thousands of astronomers gathered for the winter meeting of the American Astronomical Society in National Harbor, a shopping-center-ambiance convention center (and tourist trap,) a short distance from Washington, DC. I was only there at the beginning, leading a workshop on education for young astronomers, because I had to get back for the start of the winter quarter at Foothill College. But the cosmic news stories were descending on us thicker than the snow in the northeast in the same week.
Here are just a few of the "stellar" news items from the week:
* The Kepler mission (searching for planets orbiting other stars) announced the confirmation of several dozen planets among the thousands first glimpsed with Kepler. Among them were five rocky planets bigger than Earth. Two of them are 40% bigger than our planet and have densities similar to lead!
* Scientists working with the Spitzer Space Telescope -- which views the universe of heat rays (infra-red) and not light -- made observations of brown dwarfs (failed stars). They found that many of them have huge storms in their atmospheres (like the giant storm on Jupiter we call the "Great Red Spot.") The stormy atmospheres of these stars is what the artist's impression in the accompanying image tries to show. Such storms probably have giant lightning bolts and torrential rain. But it's too hot for the rain to be water, so the droplets could hot sand, molten iron, or salts. Bring a strong umbrella if you go.
* A graduate student at Vanderbilt University has discovered what appear to be ordinary stars that have been kicked out of our Galaxy at speeds of a million miles per hour. Such "hyper-velocity stars" have been found before, but they were thought to be a special category of big blue stars kicked out by unfortunate encounters with the monster black hole at the center of the Milky Way Galaxy. The ones in the current study come from the direction of the main disc of our pinwheel shaped galaxy, not from the the center. So what could have given them such enormous speeds is a complete mystery.
I will tell you about other discoveries in future posts. In the meantime, if you have some science background and want to see what it feels like to be a science reporter at one of these meetings, you can go to the page where the Society archives the press conferences:
http://aas.org/media-press/archived-aas-press-conference-webcasts
and check out one or two of them. Or just take a minute and contemplate how really alien and strange the worlds beyond our planet are turning out to be.
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?
