Posts Tagged ‘supernova’

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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White Dwarf Explosions and Medium Black Holes

Tuesday, September 9th, 2008 by Bellatrix

Here on Earth death usually means the end but in space, stars can have quite the interesting afterlives, and stellar corpses can even interact. The fact that stellar remnants interact is nothing new, however a new theory based on observations and computer simulations may explain a new type of supernova and help end a debate about black holes. First, let me lay out a little background.

A white dwarf is the stellar remnant of a low mass star. A star of about 2 or less solar masses will die in what is called planetary nebulae and leave behind a white dwarf. They are small dense objects about the size of earth with the mass of the sun that have an inert carbon core and are no longer do nuclear burning. For higher mass stars they die in what is called a supernova, a massive explosion where the star blows off its outer layers and leaves behind a neutron star, or if massive enough a black hole. Now there are two different kinds of supernova explosions. One is what I just mentioned, when a high mass star explodes. The other kind is when a white dwarf has a companion star. The white dwarf collects, or accretes, matter from its companion star. Once it reaches high enough mass the surface of the white dwarf reignites nuclear burning eventually then exploding in a supernova. Each one of these kinds of supernovae has a very different light signature, or spectrum.

A new paper was published describing a new way of igniting a white dwarf and a new type of supernova. In this new process a white dwarf wanders too close to a black hole. The strong gravity of the black hole causes tidal disruption in the white dwarf, it pulls and flattens the white dwarf into a pancake shake, and this compresses the star’s material reigniting nuclear burning. As each section of the star is squeezed through a point of maximum compression, the extreme pressure causes a sharp increase in temperatures, which triggers explosive burning. The explosion ejects half the material from the star while the rest falls into the black hole. This in-falling material heats up and gives off x-rays. So this supernova should have a different spectrum and be followed up by a glow of x-rays.

Now the interesting thing is this process would only be possible with a black hole of a particular mass, neither too big nor too small. It would have to be between 500 to 1000 solar masses. Theoretically and observationally we only know of small black holes, several solar masses, or super massive ones on the order of millions of solar masses. So proof of this process would mean there are intermediate mass black holes, which would beg the question of where do these black holes come from?

These types of supernova are thought to be 100 times less frequent than the other types of supernova. The Synoptic Survey Telescope, planned for 2013, will be observing hundreds of supernova per year. So far this new process between white dwarfs and black holes has been successfully modeled with computer simulations, but hopefully with this new telescope we will be able to observe the spectrum of these supernova. This would provide proof for this theory, answer some questions, and lead to some new ones.

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