What if multiple astronomical instruments were trained on the same short duration event? Since most events like that happen without warning, it would be very rare for different instruments to do that. This post is about such an event. It describes the connection between a radio telescope near my home and a black hole involved in this event. The telescope is in the center of this picture. It is 25 meters in diameter and a mere 4 miles away from my backyard. It’s part of the VLBA Very Long Baseline Array and is operated by the U of Iowa Dept. of Physics and Astronomy.
The Very Long Baseline Array (VLBA) includes ten radio telescopes from Hawaii to the Virgin Islands spanning 5,351 miles. It’s one of the world’s largest dedicated telescope arrays. If your eyes could see as sharp as this array, you could read street signs in NYC from LA. The VLBA helps astronomers measure mass, makeup, and movement of cosmic objects.
A few years ago I got a tour of the telescope with a group of physics teachers when it was shut down. It was pointed straight up. We climbed up the stairs and ladders, went through the small room housing detectors, and emerged through a small trap-door hatch. What a thrill to stand in the bowl of the 82 ft parabola with nothing in view but the sky above.
The 10 telescopes observe the same objects all at the same time such as blazars, quasars, black holes, dying stars, pulsars, exoplanets, and masers. What these objects have in common is the emission of radio frequency waves. Atomic clocks at each telescope are synchronized. The timing of the reception of the radio signals is then combined to produce a synthesized telescope with a 5,351 mile aperture. In astronomy, the wider the aperture, the finer the detail that can be resolved. For more specific information on radio interferometry, follow this link. The subject of interest for this post is a Black Hole that emitted what looked like a cosmic fart.
Black Hole Accretion Disks and Gas Jets
In mid-2009, there was an outburst of a binary system known as H1743–322, located about 28,000 light-years away toward the constellation Scorpius. The system has a normal star (red) and a black hole orbiting each other in a matter of days. In close arrangements like that, the black hole pulls a stream of matter into it from the star. The flowing gas forms a flattened accretion disk (blue) millions of miles across around the black hole. As a note of reference, Earth is 93 million miles from our Sun. The disk is compressed and heated to tens of millions of degrees and emits X-rays. Some of the matter gets redirected and is emitted as jets streaming away from the black hole following twisted magnetic field lines along the axis of spin. Click on the image for an animation of the process. Dial-up users, you may not want to do that. It is a large file.
The jets normally are a steady flow of particles. Sometimes, they have huge outbursts that throw large energetic gas blobs at significant fractions of the speed of light. The image at the right is the jet directed toward the upper right from object M87. There are some energetic blobs, or knots, of gas seen along the path of the jet. Thirteen years of observations from by the Hubble Space Telescope have determined this jet is 5,000-light-years long and is moving as captured in this video. The jet of superheated gas comes from a supermassive black hole in the center of elliptical galaxy M87.
In early June 2009, H1743–322 underwent a transition ourburst and emitted blobs of gas out in opposite directions while astronomers were watching…
…with RXTE, the VLBA, the Very Large Array near Socorro, N.M., and the Australia Telescope Compact Array (ATCA) near Narrabri in New South Wales. The observatories captured changes in the system’s X-ray and radio emissions as the transformation occurred. From May 28 to June 2, the system’s X-ray and radio emissions were fairly steady. RXTE data show that cyclic X-ray variations, known as quasi-periodic oscillations or QPOs, gradually increased in frequency over the same period. On June 4, ATCA measurements showed that the radio emission had faded significantly.
RXTE is the Rossi X-ray Timing Explorer satellite that observed the high-energy worlds of black holes, neutron stars, X-ray pulsars and bursts of X-rays. After 16 years of amazing discoveries, the RXTE mission was decommissioned on January 5, 2012.
How The Observations Fit Together
The RXTE spacecraft had observed in the H1743–322 system a ‘tell-tale heart’, or heartbeat, of x-ray emissions. The unique feature of this system was how the frequency of the heartbeat had been increasing steadily from May to June 2, 2009. By June 4, 2009, the x-ray feature had stopped. The heartbeat stopped. At the same time, astronomers with the VLBA were observing the radio emissions of H1743-322. They were amazed to see the event unfold before their telescopes’ eyes.
The same day that the radio emission increased, an extremely detailed VLBA image revealed a bright, radio-emitting bullet of gas moving outward from the system in the direction of one of the jets. On June 6, a second blob, moving away in the opposite direction, was seen.
As you watch the video above, the animation shows the circulating material in the accretion disk increasing in frequency as evidenced by the RXTE data. It is followed by the massive ejection of two blobs of gas in opposite directions as evidenced in the VLBA data. For the first time, astronomers have witnessed this kind of event in detail. Below is a graphic of the final days of the event showing the observations of VLBA across top and RXTE data across the middle on the same dates. The disappearance of the QPOs after June 2 coincides with the formation of the radio emitting blobs detected by VLBA. The third row is the corresponding part of the above video animation. The graphic is small and hard to read. Click on it to see the full sized big jpg from NASA.
Rarely do astronomers get to have multiple instruments trained on the same short duration event. This one played out well. And, it is a significant syzygy for me because it’s as if it happened right in my own backyard. I hope you enjoyed it, too.