Archive for June, 2009

Ghosts Lurking from Massive Black Hole

Thursday, June 4th, 2009 by Bellatrix

We all know that super massive black holes lurk in the center of galaxies. We know that they can have strong impacts on the surroundings; usually we can see how things are being impacted by the outflows of energetic particles being ejected from feeding black holes. However, if a black hole is not active and does not have jets usually we cannot see anything left over, any remnants from its energetic past. Well recently using the Chandra X-ray observatory a ghost of an eruption from a massive black hole has been observed and may have some interesting things to tell us.

The X-ray ghost, so-called because a diffuse X-ray source has remained after other radiation from the outburst has died away, is in the Chandra Deep Field-North, one of the deepest X-ray images ever taken. The source HDF 130 is over 10 billion light-years away a time when galaxies and black holes were forming at a high rate. Scientists think the X-ray glow from HDF 130 is evidence for a powerful outburst from its central black hole in the form of jets of energetic particles traveling at almost the speed of light. When the eruption was ongoing, it produced large amounts of radio and X radiation, but after several million years, the radio signal faded from view as the electrons radiated away their energy.

However, less energetic electrons can still produce X-rays by interacting with the pervasive sea of photons remaining from the cosmic background radiation. Collisions between these electrons and the background photons can impart enough energy to the photons to boost them into the X-ray energy band. This process produces an extended X-ray source that lasts for another 30 million years or so.

This is the first X-ray ghost ever seen after the demise of radio-bright jets. Astronomers have observed extensive X-ray emission with a similar origin, but only from galaxies with radio emission on large scales, signifying continued eruptions. In HDF 130, only a point source is detected in radio images, coinciding with the massive elliptical galaxy seen in its optical image. This radio source indicates the presence of a growing supermassive black hole.

The power contained in the black hole eruption was likely to be considerable, equivalent to about a billion supernovas. The energy is dumped into the surroundings and transports and heats the gas. Because they’re so powerful, these eruptions can have profound effects lasting for billions of years.

The data tells us that there should be many more such ghosts lurking around out there, especially if black hole eruptions are as common as are thought in the distant universe. This is a good discovery as it tells us that we do not have to catch a black hole in the act to witness the big impact they can have. Using Chandra I’m sure searches will begin for other such remnants. Once we have found more of them we can search for patterns in the data, see if there are commonalities in these eruptions or links between the data and other such things such as the mass of the black hole. 

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Old Method Finally Yields Results

Monday, June 1st, 2009 by Bellatrix

Modern develops in hunting for planets outside of our own solar system have yielded the discovery of well over a hundred different planets now. These newer methods include very new telescopes with the resolving power of being able to actually see an exoplanet, with which only 1 so far has been confirmed photographed, and other methods include using radial stellar velocity, or the Doppler effect, and the transit method. Now for the first time since its inception 50 years ago the method of astrometry has found an exoplanet.

The method of astrometry was first thought of 50 years ago to search for planets outside our solar system, called exoplanets. It involves measuring the precise motions of a star on the sky as an unseen planet tugs the star back and forth. But the method requires very precise measurements over long periods of time, and until now, has failed to turn up any exoplanets. This method is different from the more commonly used method of using the Doppler Effect or radial velocity of a star. Most exoplanets have been detected by watching for a wobble of a star, a gravitational tug from an orbiting planet due to the Doppler Effect. Astrometry also looks for a wobble but it is different  it measures the displacement the planets cause in their parent star’s apparent position on the sky, due to their mutual orbit around the center of mass of the system.

Two astronomers from NASA’s jet propulsion laboratory in California have been collecting data for the past 12 years from an instrument mounted on a telescope at the Palomar Observatory near San Diego. After looking at data from 30 different stars they have finally found what they were looking for: a planet surrounding the star VB 10. The planet itself is about 6 times the mass of Jupiter and an orbit a bit farther out making a cold Jupiter.  The star itself is quite small, a dwarf, at only 1/12 the mass of the sun. For a long time VB 10 was known as one of the smallest stars and now is the smallest star with a planet around it.  Because the star is so small, its planetary system would be a miniature, scaled-down version of our own. For example, VB 10b is located about as far from its star as Mercury is from the Sun. Any rocky Earth-sized planets that might happen to be in the neighborhood would lie even closer in.

The finding confirms that astrometry could be a powerful planet-hunting technique for both ground- and space-based telescopes. For example, a similar technique would be used by SIM Lite, a NASA concept for a space-based mission that is currently being explored. This is an exciting discovery because it shows that planets can be found around extremely lightweight stars. It seems that nature likes to form planets, even around stars quite different from our Sun. Now that it’s proven that this technique actually works and yields results it seems likely others might take it up, and more exoplanets will be found. One more tool in the planet hunter’s arsenal; one step possibly closer to finding a planet like our own.

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