Posts Tagged ‘brown dwarf’

Little Stars with Jets

Monday, September 29th, 2008 by Bellatrix

There are many objects in the universe that have jets of material exploding from them. A few examples are neutron stars, black holes, quasars, and protostars. Well now we can add brown dwarfs to that list. One wonders what causes these jets and if brown dwarfs can have them what’s next?

A brown dwarf is like a failed star. It’s cool and small, with a mass range of between 10 to 90 Jupiter masses. These objects are not massive enough to start nuclear burning like normal stars. They can be hard to observe since they are so small and don’t give off nearly as much light as a normal star. There is some debate about how to distinguish a brown dwarf from a giant planet like Jupiter. There are some differences; they all have about the same radii so if the mass is higher than about 10 Jupiter masses, they have a higher density and are usually not considered a planet. Also with brown dwarfs water is always found in a gaseous state where in giant planets it condenses to ice; also planets usually have ammonia in their atmospheres while brown dwarfs do not.

Now the brown dwarf called 2MASS1207-3932 has a mass of about 24 Jupiter masses with a companion planet of about 5 Jupiter masses. This brown dwarf also has a disk around it like that seen in young stars. This is the smallest object ever observed to have a jet. The jet is moving at a speed of a few kilometers per second and stretches about 1 billion kilometers; it is also much smaller and less bright than jets seen in regular stars. Astronomers had observed jets from one other brown dwarf, so with this new discovery a pattern is emerging. Its discovery suggests that these brown dwarfs form in a similar manner to normal stars but also that outflows are driven out by objects as massive as hundreds of millions of solar masses down to Jupiter-sized objects.

Astronomers were not able to observe the jets directly. Astronomers had to use the powerful Very Large Telescope (VLT) , and only an instrument called UVES could provide the sensitivity and resolution required to “see” the jet. The results highlight the incredible level of quality of instruments available today. With ever more powerful and sensitive instruments we are observing more of these faint objects and are able to learn much more about brown dwarfs, their properties, and how they develop.

This discovery tells us more about the development of brown dwarfs, but also raises some new questions. Does this mean that giant planets also have jets that we haven’t detected yet? If not, why not? What is the cut off threshold between the two? Also, what role exactly do these jets play in the life of the brown dwarf? If not all brown dwarfs have jets, what are the resulting differences between ones that do and ones that don’t? Hopefully, as we are able to observe more of these objects with our better instruments we will learn the answers to these questions.

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Update on Extrasolar Planet Hunting

Wednesday, September 17th, 2008 by Bellatrix

So as fate would have it two days after writing my most recent blog entry, an article was published with the title “First Picture of Planet around Sun-Like Star”. In my previous blog post I mentioned how we had only indirectly observed planets around other stars and had yet to photograph one directly. Well first I must say that even before this new discovery, my statement was not entirely correct. Some people within the last year have claimed that they had photographed planets around stars. I did not mention it because the jury is still out on these pictures as to whether or not what is seen is actually an orbiting planet or perhaps just a background object.

However, even with those couple of photos floating around, this new one is slightly more interesting. Those few photos we have so far of possible planets have all been around very dim stars called red dwarfs or even dimmer brown dwarfs. This new picture is of a star that is very much like our sun. The planet observed is giant (about eight times the mass of Jupiter) and lies far out from its star (about 330 times the Earth-Sun distance). It’s large mass, or size, is one the key factors in being able to view it directly. This planet is extremely far out from its host star; for frame of reference, Neptune is our farthest planet and lies only 30 times the earth-sun distance.

The discovery was made by the Gemini North Telescope on top of Mauna Kea, which is associated with the previously mentioned Subaru Telescope. However, more studies will have to be done to prove this object is in fact orbiting the observed star, but evidence from the indirect method of detection supports the idea that this is not just a background object in the picture.

Given the distance to its star and other strange qualities such as its large mass and hot temperature (about 1500C compared to Jupiter at 110C), we may have to really start looking at our models of planet formation. Currently our theories would not predict, or allow for, such a planet to be where it is and how it is. For those who want to see the pretty picture of the planet, Google the star name 1RXS J160929.1-210524 (nice name huh?) or should be available from the Gemini observatory’s website.

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