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.
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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/
This week, 2800 astronomers are gathered in Southern California for the winter meeting of the American Astronomical Society and the news from the meeting is coming so fast and furious even seasoned astronomy fans are somewhat overwhelmed. Let me just list a few of the news stories for you for now and we will explore some of them further in future posts.
The picture I have attached above shows new information about the planet orbiting the star Fomalhaut, the 17th brightest star in the night sky (and, at a distance of only 25 light years, one of the closer stars to us.) The faint distant planet, one of the first planets outside the solar system to be actually photographed, is shown here in an image from the Hubble Space Telescope.
In the image, the bright star has been covered up by a dark disk (in the middle) that the Hubble telescope can use to block light. That allows us to see the planet and the huge dusty disk surrounding the star. The planet has an orbit that takes it around its star in about 2000 Earth years. (Compare that to a 1-year orbit for Earth and a 12-year orbit for Jupiter.) So some astronomical commentators are suggesting it might be more of a giant comet or a distant ice-dwarf (like Pluto) and not really the kind of planet we first think of when we talk about planets.
In a related story, the Kepler mission team, searching for planets that "eclipse" their stars (see earlier posts of mine on this mission), is reporting 461 new planet candidates, bringing their total number of possible planets to 2,740! Four of the new candidates are less than twice the size of Earth and orbiting where conditions are Earth-like.
Nest, teams of astronomers using orbiting telescopes have filed the most detailed "weather report" yet about clouds in the atmosphere of a "brown dwarf" -- the name we give to a failed star. These objects begin life like stars do, but can't keep making energy in the way our Sun and others stars can. It's amazing that we can now probe for the existence of Earth-sized clouds in the outer layers of these remote, faint objects.
Plus there is the possible discovery of floating icebergs on Saturn's moon Titan, an asteroid belt around the bright star Vega, and much more. (The reason there is so much news all at once is that astronomers save their discoveries for announcement at this annual winter meeting, so they can share the results with their colleagues and argue about them right then and there. With almost 3000 astronomers gathered in the same convention center, there is a good clump of experts to dissect and admire each discovery.)
More details in posts to come.
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