Astronomers may have caught a black hole by eating a star

The SS 433 is a microquasar, consisting of a compact object (right), which is a black hole or a neutron star, sucking the matter from its companion star (right).
(Credit: illustration of the artist by NASA)

At vast cosmic distances, supermassive black holes, called quasars, engulf the matter in accretion discs that shine so brightly that they dominate the light of entire galaxies. Closer to home, compact objects called microquasars provide astronomers with insight into the processes at work in far-off behemoths. Now, an international collaboration of researchers announced in the journal Nature that they had detected the first gamma ray signal emitted by the ends of the two jets spouting from a microquasar of the Milky Way.

Give me a boost

The microquasar they observed, SS 433, is either a black hole or a neutron star in a binary system located about 15 000 light-years from Earth. While it aspires the matter from its ordinary stellar companion, the SS 433 is not only surrounded by a hot and swirling accretion disk, it also projects throws at 26% of the speed of light. SS 433 is one of about 12 microquasars identified from the Milky Way, and one of the few among which gamma rays – an extremely intense light – have been seen.

Even though microquasars are in our own galaxy, they are still small and hard to see. But "The SS 433 is fine in our neighborhood," said Jordan Goodman of the University of Maryland, also a senior researcher and US spokesman, in a press release, about the collaboration between the Observatory of high-temperature gamma rays Cherenkov Water Cherenkov. "Thus, thanks to HAWC's broad, unique field of view, we were able to resolve both microquasar particle acceleration sites." These two sites are the ends of the microquasar jets, where researchers believe that Electrons interact with the light of the cosmic microwave background. (CMB), which permeates the universe, is responsible for gamma rays. This process, called reverse-Compton scattering, amplifies CMB photons normally from low energy up to the extremely high energies of gamma rays.

This is a new way to produce high energy gamma rays in microquasars. The discovery was made possible by the fact that the SS 433 jets are not directed directly at the Earth, which allows astronomers to locate the two different ends of the jets, which is not possible when the jets of an object are directed to us rather than to the side.

"The SS 433 is an unusual star system and every year, something new has appeared," said Segev BenZvi of the University of Rochester, and co-author of the study.

Blue Light Special

To make the discovery, the team used more than 1,000 days of data from the HAWC Observatory in Puebla, Mexico. HAWC can study about 15% of the sky at a time, looking for "showers" that result from the infiltration of gamma rays and cosmic rays into the atmosphere and a loss of energy when they bounce among the molecules air. HAWC uses over 300 steel tanks 13 feet (4 meters) high and 24 feet (7.3 meters) in diameter filled with water. When the particles of an air shower reach the water, they generate a Cherenkov radiation, which is a blue glow that occurs because the particles travel faster than the speed of light in the air. 39 water, which is less than the speed of light in the vacuum or air. . (Think of the same process that creates a sonic boom, but for the light, not for the sound.) The detectors inside the tanks look for that glow, recording it so that the researchers can determine what is happening. where it comes from.

From the microphone to the quasar

The quasars are large and bright, but also very far apart, which means that they are more difficult to study than objects closer to the Earth. Microquasars are smaller and closer – and because they are smaller, they change much faster, making it easier to graph what's going on inside. What can take months or years in a quasar can happen in a few hours or days in a microquasar. Research has shown that these systems can then be developed to learn about their massive counterparts in other galaxies.

But "to look at only one type of light coming from the SS 433, it's like seeing only the tail of an animal," said co-author, Ke Fang, of Stanford University. "So, we [will] combine all its signals, from low energy X-ray radio, to new high-energy gamma ray observations, to determine the type of SS 433 beast. "

And from there, "we can improve our understanding of particle acceleration in SS 433 and its giant extragalactic cousins, called quasars," said Goodman.