A hungry black hole devoured a star, and the ‘burp’ shows how the chowed down

An artist’s impression of material falling into a black hole and the resulting jet is prepared.

(L. Calçada/ESO)

A black hole that is gobbling a great meal is providing an insight into how the black holes that matter to devour and influence on the evolution of galaxies.

The researchers found that the X-ray burst signal is caused when a black hole shredded a passing star, was repeated in the radio-wavelengths almost two weeks later. The radio echo is most likely to come from an exodus of high-energy particles streaming from the black hole, the researchers said.

In 2014, Las Cumbres Observatory’s All-sky Automated Survey for Supernovae, a collection of robotic telescopes located around the world, picked up signals from 300 million light-years away. The event, known as ASASSN-14li, has occurred as a star to shreds was torn, and after passing too close to a black hole. Multiple telescopes immediately turned to the track of the tidal disruption flare, a powerful burst of electromagnetic energy caused by the destruction. After poring through about six months worth of data, Dheeraj Pasham, a researcher at the Massachusetts Institute of Technology, and Sjoert van Velzen, of the Johns Hopkins University, found a pattern in the radio wavelength, which are almost duplicates of the X-ray signal. [No Escape: Dive Into a Black Hole (Infographic)]

“This tells us the black hole feeding rate is the controlling force of the jet produces,” Pasham said in a statement. “A well-fed black hole produces a strong beam, while a malnourished black hole, producing a weak jet or no jet. This is the first time that we have seen of a radius that is controlled by a feeding supermassive black hole.”

More Of

  • The event

  • No Escape: Dive Into a Black Hole (Infographic)

  • X-ray emissions

  • The Astrophysical Journal

No coincidence

If a star comes too close to a black hole, the huge mass of the black hole exerts a tidal pull on the star. The forces are so strong that they can stretch and flatten the stars, eventually tearing it to pieces. The stellar debris falls toward the black hole, where it is collected in the accretion disk, the collection of material that feeds the black hole. This is what happened in the case of ASASSN-14li.

The feeding process generates huge energy is visible in several wavelengths. Flares have been observed and other black holes in the optical, uv, x-ray and radio wavelengths. If ultrahot material in the inner regions of the accretion disk funnel in the direction of the black hole, it produces an X-ray emission, while the material produces optical and uv emission. The source of radio emissions, however, remained unknown.

“We know that the radio waves that come from really energetic electrons that move in a magnetic field — that is a process,” Pasham said. “The debate is, where are they really energetic electrons come from?”

One possibility is that, in the moments after the stellar explosion, a shock wave moves outward, energetic plasma particles and causing them to radio waves. These radio waves would look very different from the pattern of X-rays created by the infalling stellar material. But the signal Pasham and Van Velzen found in the radio is a 90 percent match with the X-ray signal.

“What we have found, in principle, challenges this paradigm,” Pasham said.

The close match suggests that the sources that are responsible for creating the radio waves and x-rays are related.

“It is no coincidence that this is happening,” Pasham said. “It is clear that there is a causal link exists between this small region the production of X-rays and this great region is the production of radio waves.”

The few sets that the radio waves are created by high-energy particles streaming from the black hole soon after the behemoth begins to absorb the material from the shredded star. Because the radio waves are formed in a region tightly packed with other electrons, most of the signal was absorbed by the particles, the researchers said. The electrons responsible for the radio signal can only escape if they traveled downstream of the jet, producing the signal that the scientists discovered.

The researchers concluded that the strength of the jet must be controlled by the accretion rate, or the speed at which the black hole is the consumption of the stellar debris is responsible for the transmission of X-rays.

The new observations, which were published March 19 in The Astrophysical Journal, scientists can better characterize the physics of the jet behavior. This, in turn, can help improve the researchers to understand how galaxies develop.

Galaxies grow by producing new stars, but only under very cold temperatures. Jets emitted by black holes, heat from the surrounding galaxies, and the temporary stop of stellar births. Pasham, said the team is the new understanding of the jet production, and black-hole growth can help to simplify models of the evolution of galaxies.

“If the speed at which the black hole is feeding is proportional to the speed at which the pumps of energy, and if that really works for each black hole, it is a simple recipe that you can use in the simulations of the evolution of galaxies,” Pasham said. “So this is intimated in the direction of a greater whole.”

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