Posts Tagged ‘quasar’

Microquasars: Black Holes and Normal Stars an Interesting Mix

Tuesday, December 2nd, 2008 by Bellatrix

Astronomers using two different telescopes and two different systems have started learning about microquasars. They’re learning new things that can then hopefully be applied to full size quasars as well.

A quasar is an extremely powerful, luminous and distant active galactic nucleus. While there was initially some controversy over the nature of these objects, there is now a scientific consensus that a quasar is a compact region surrounding the central supermassive black hole of a galaxy. Quasars show a very high redshift, meaning they are located a great distance from us. Quasars are active because the central black hole is accreting a lot of material. Near the black hole, intense magnetic fields in the disk accelerate material into tight jets that flow in opposite directions away from the hole.

Microquasars is a two-body system consisting of a stellar mass size black hole and a star, usually a red giant. The giant star is feeding material to the black hole. Which, needless to say creates some interesting dynamics. Astronomers have been looking at two systems, Swift1753.3-0127 and GX339-4, with the European Southern Observatory’s Very Large Telescope and NASA’s Rossi X-ray Timing Explorer to study microquasars. Microquasars are not only closer but change more rapidly, so a process that may take a normal quasar a year to undergo might only take a microquasar a few minutes.

Astronomers had thought that the visible light emission coming form microquasars was coming form far out in the accretion disk and thus did not give much information about the main actions going on. However, they were wrong. They now know that the optical and x-ray emission are intrinsically linked, probably by the same immense magnetic fields that hurl material into near light speed jets.

The data shows that light output typically drops just before x-ray output undergoes a large spike. The rapid variations in the x-ray and optical emission must have a common origin. The cool thing about discovering such patterns that stand out amidst chaotic fluctuations of light is that they give us a new handle on understanding the underlying physics. The best candidate is the strong magnetic fields as the dominant process behind it all.

So again what we once thought was wrong, we learned something new, but realize how much we don’t know yet. This data is a new clue about very mysterious and not yet understood systems. We still don’t know exactly what’s going on in these dynamic systems, but we have one more piece of the puzzle.

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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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