Artist's concept of the unusual X-ray transient Swift J1644+57. Scientists have witnessed the birth of a relativistic jet from a tidally disrupted star near the event horizon of a supermassive black hole. The highly variable X-ray emission present at early times likely comes from a distinct region (blue) from the radio emission (red). This highly energetic event was beamed towards the Earth.
Credit: Amadeo Bachar
Images from Swift's Ultraviolet/Optical (white, purple) and X-Ray telescopes (yellow and red) were combined to make this view of Swift J1644+57. Evidence of the flares is seen only in the X-ray image, which is a 3.4-hour exposure taken on 28 March 2011.
Credit: NASA/Swift/Stefan Immler
ESSEX: The process of a star being broken apart and swallowed by a supermassive black hole has been observed from start to finish for the first time.
Two groups of researchers have published data from NASA's Swift satellite to present astronomers with a rare opportunity to study the birth of a relativistic jet - a high-speed outflow of ionised matter that has been launched into space by the material from a disrupted star.
Scientists have seen the aftermath of this event many times before, but have never seen the destruction from the onset. The source of the high-energy emissions has been named Swift J1644+57. It has been identified as a previously dormant black hole in the Draco constellation 3.9 billion light years from Earth.
"Incredibly, this source is still producing X-rays and may remain bright enough for Swift to observe into next year," said one of the lead authors of the papers published in the current issue of Nature, David Burrows from Penn State University, lead scientist for the mission's X-Ray Telescope instrument. "It behaves unlike anything we've seen before."
Curiosity kills more than the cat
Most galaxies possess a central supersized black hole weighing millions of times the Sun's mass, including our own, which was confirmed in 2008 by German astronomers.
The innermost gas in the disk spirals toward the black hole, where rapid motion and magnetism create dual, oppositely directed 'funnels' through which some particles may escape. Jets driving matter at velocities greater than 90% the speed of light form along the black hole's spin axis. In the case of Swift J1644+57, one of these jets happened to point straight at Earth.
According to the new studies, the black hole in the galaxy hosting Swift J1644+57 may be twice the mass of the four-million-solar-mass black hole previously discovered in the centre of the Milky Way galaxy. As a star falls toward a black hole, it is ripped apart by intense tides. The gas is corralled into a disk that swirls around the black hole and becomes rapidly heated to temperatures of millions of degrees.
Both the star and the black hole are billions of years old. The star would have been travelling around the galaxy all that time and unfortunately wandered too close.
Targeting gamma rays
The new observations were first made by the Swift satellite on 28 March 2011. At that stage Burrows had reported a bright X-ray flare from an extragalatic object. From the flare's spectral signature and the time evolution, his study concluded that it comes from the accretion of material onto a million-solar-mass black hole.
Lead author of the second paper, Ashley Zauderer of the Harvard-Smithsonian Centre for Astrophysics in Cambridge's focus was to target gamma ray bursts that are detected by Swift. "All evidence started pointing towards a tidally disrupted star - initially, we just thought that this source was a normal gamma ray burst with some strange features," he said.
He added that it was clever technology and an extraordinary team effort that were responsible for the rapid response time of this discovery. "We get text message alerts on our cell phones from the Swift satellite when it detects a source of gamma ray emission above a certain threshold. This allows us to submit our scripts to radio facilities within minutes."
