Scientists have long believed that the most energetic gamma rays in space are forged in the intense furnaces of very active supermassive objects. black holesfar, very far. But a new study has traced some of these high-energy photons to an object much closer to us.
V4641 Archers is a system located approximately 20,000 light years from Earth, in the direction of the constellation Sagittarius. There, a black hole with the mass of about six Suns, sucks up material from a giant star of about three solar masses – and produces intense radiation like a cosmic particle accelerator.
Astronomers have now detected photons from V4641 Sagittarii carrying energies of up to 200 teraelectronvolts (TeV). For reference, that’s 200 trillion times more energy than visible light, and among the highest energy photons you will discover it in space.
Gamma rays around this energy level are known to travel throughout the cosmos, but scientists thought they came primarily from quasars – bright galactic cores, in which supermassive black holes release enormous amounts of energy when they disorderly absorb falling gases.
V4641 Sagittarius is what we call a microquasarand as the name suggests, it functions sort of like a mini version of a regular quasar. THE black hole is smaller, the source of matter is smaller and the radiation they emit is smaller. Or at least that’s what conventional thinking told us.
“Photons detected by microquasars generally have energies much lower than those of quasars,” said Sabrina Casanova, from the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN).
“Usually, we talk about values of the order of tens of gigaelectronvolts. In the meantime, we have observed something quite incredible in the data recorded by the detectors of (High altitude water Cherenkov) observatory: photons coming from a microquasar located in our galaxy, and yet carrying energies tens of thousands of times higher than normal.”
Located on the flank of the extinct Sierra Negra volcano in Mexico, the HAWC gamma-ray observatory is designed to capture particularly energetic particles from space. To do this, it is made up of 300 large steel tanks filled with purified water.
The idea is that when these high-energy particles enter a tank, they trigger a cascade of other particles that move through the water faster than light. This creates a flash of light called Cherenkov radiationwhich is essentially the electromagnetic version with a sonic boom.
Sensitive detectors inside the tanks capture these flashes and allow scientists to work backwards to determine what type of charged particle triggered them and from what direction they came.
HAWC can see 15 percent of the sky at any given time, and will scan two-thirds of the entire sky every 24 hours, creating a sort of cosmic map. It was on one of these cards that V4641 Sagittarii appeared as an unexpected bright spot of gamma rays.
“While examining sky maps in search of my next project, I noticed a region five degrees from our galactic plane with light emissions that had not been visible in previous data sets.” said physicist Xiaojie Wang.
“No gamma ray sources have been identified or analyzed in this region. So I seized the opportunity and led the analysis.”
Upon closer inspection, V4641 Sagittarii was found to be the source of these ultra-high energy gamma rays. Other microquasars, such as SS 433have already been detected emitting photons at energies above 25 TeV, but V4641 Sagittarii is next level: it produced radiation comparable to that of ordinary quasars, a feat previously thought impossible.
The new discovery allows astronomers to better understand not only cosmic radiation, but also quasars themselves. The physics around these huge objects happens in slow motion, over millions of years – but microquasars carry out similar processes on timescales of days. They are like natural simulators.
The research was published in the journal Nature.
