18 December 2013

NASA’s Swift discovers 100,000 super-massive black holes till now

When the X-Ray Telescope (XR) on board NASA’s Swift Gamma-Ray Burst Mission scans the sky, it is looking mostly to supplement the satellite’s more important instruments. As the name implies, the Gamma-Ray Burst Mission is focused mostly on the action of its gamma-ray detecting Burst Alert Telescope the attached XRT is mostly there to view the X-ray afterglow that follows many gamma burst events. However, Swift is not an acronym but a descriptor for one of NASA’s most agile sky viewers: as its autonomous robotic platform twists to bring event after event into view, Swift’s wide-angle X-ray lens passes over large portions of the sky.

Never ones to waste perfectly good telescope time, scientists have spent more than eight years compiling and analyzing this mass of incidental data, and this week researchers from the University of Leicester released their initial findings: Swift has found almost 100,000 new major X-ray sources, and these scientists believe that most of them represent the super-massive black holes at the centers of our universe’s largest galaxies. These come from more than 150,000 high-energy X-ray sources found, and those that aren’t black holes are under equal scrutiny by astronomers of all stripes. More transient X-ray sources than galactic cores are attributed to things like stellar flares and supernovae.

Swift’s X-ray readings in the aggregate.

As material like gas is drawn into a black hole, neutron star, or any other ultra-heavy gravitational attractor, it begins to move faster and faster, compress, and heat up. The gas is being accelerated and pressed into a smaller space, and strong magnetic fields also help to speed up their electrons. All this works together to ramp the electrons up to extremely high speeds, eventually ejecting a photon in the X-ray portion of the EM spectrum (among other places). Swift isn’t just quick at collecting these readings, either. When the data center back on Earth receives new readings from the satellite, it can have those up and visible to the world within minutes.

A super-massive black hole can get up to millions or even billions of solar masses. There are only (“only”) about 300 billion stars in the Milky Way, meaning that such an object could itself contain some significant fraction of the mass of an entire galaxy. In the galaxy Perseus, astronomers last year observed a black hole some 17 billion times heavier than our Sun, or about 3% the estimated mass of the Milky Way. Most astronomers believe that there is one or more black holes at the center of normal galaxies, but they’re difficult to detect because of the galactic core’s other powerful sources of radiation. Sagittarius A* is a point at the center of our galaxy that is widely believed to be a super-massive black hole.

This is an example of what Swift sees in a particular patch of sky.

Swift launched in 2004 to look at the bursts of gamma radiation that pierce the sky roughly once per day. They are the most energetic of the electromagnetic rays and they represent the universe’s most violent events. From supernovae to the Big Bang itself, gamma radiation is our window into the cataclysms that have made the universe what it is today. Mapping these events, and exploiting their high-energy signals to look into other phenomena, is important. The Swift mission uses three different cameras to look at these events from their gamma rays signatures all the way down to the ultraviolet and visible light that accompanies them.

This new info seems to confirm what many scientists already thought about the origin of galaxies, but also provides astronomers with a helpful map of the skies and an incredibly detailed view of the universe’s most unique and violent events.

Now read: Sleeping Supermassive Black Holes Can Have Periods Of Intense Flare-Ups


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