cosmic outburst

Watch two jets burst from a black hole at 80% the speed of light

The explanation for it may break your brain.

X-ray: NASA/CXC/Université de Paris/M. Espinasse et al.; Optical/IR:PanSTARRS

At the center of galaxies, massive black holes lurk in the shadows and, usually, they swallow up material that dares to come near. However that's not always the case, new images captured by astronomers show what happens when a black hole acts as a gas fountain.

Astronomers have recently caught a startling glimpse at two hot gas jets bursting from a stellar-mass black hole at 80 percent the speed of light, creating a hypnotic cosmic flare that further fuels our fascination by these massive beings.

A team of astronomers recorded four observations by NASA's Chandra X-ray Observatory taken in the years 2018 and 2019, allowing them to detect the jets as they burst from the black hole, shooting away from its center and slamming straight into surrounding matter.

The observations are detailed in a study published recently in The Astrophysical Journal Letters.

The black hole in question is located about 10,000 light years away in the Milky Way and has a lone companion star that measures about half the mass of the Sun. It is a stellar-mass black hole, meaning that it formed in the aftermath of the gravitational collapse of a star. Therefore, this black hole is tiny compared to others, measuring at about eight times the mass of the Sun.

That may seem big, but considering that the supermassive black hole at the center of the Milky Way, Sagittarius A*, is 4 million times the mass of the Sun, it's relatively quite small.

But this small black hole still put on quite a show.

The event horizon marks the boundary around a black hole from which nothing, not even light, can escape. However, while hot gas from the surrounding star falls into the black hole, some of the hot gas shoots out in the form of jets, or short beams of material, from outside the event horizon.

The jets are pointed in opposite directions, moving away from the black hole toward the north and the south.

From our perspective on Earth, it appears as though the northern jet is moving at 60 percent the speed of light, while the southern one is traveling at 160 percent of light speed. However, that is impossible: The speed of light is defined as 186,282 miles per second, and nothing can travel as fast as, and surely not faster than, the speed of light. If an object were to try to travel at the speed of light, its mass would become infinite.

The reason why the southern jet seems to be traveling faster than the speed of light is the result of an optical illusion given our Earthly perspective. The southern jet is pointed in our direction, and if something travels towards us near the speed of light along a direction close to our line of sight then that means it is traveling almost as quickly towards us as the light it generates. Therefore, it gives the illusion that it is traveling faster than the speed of light.

But in reality, the velocity of the particles in both jets is greater than 80 percent of the speed of light. So it is not quite breaking the rules of physics, but still very close.

Abstract: The black hole MAXI J1820+070 was discovered during its 2018 outburst and was extensively monitored across the electromagnetic spectrum. Following the detection of relativistic radio jets, we obtained four Chandra X-ray observations taken between 2018 November and 2019 May, along with radio observations conducted with the VLA and MeerKAT arrays. We report the discovery of X-ray sources associated with the radio jets moving at relativistic velocities with a possible deceleration at late times. The broadband spectra of the jets are consistent with synchrotron radiation from particles accelerated up to very high energies (>10 TeV) by shocks produced by the jets interacting with the interstellar medium. The minimal internal energy estimated from the X-ray observations for the jets is ∼1041 erg, significantly larger than the energy calculated from the radio flare alone, suggesting most of the energy is possibly not radiated at small scales but released through late-time interactions.
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