A black hole ripped apart a star in a galaxy far, far away

It was an event not seen in over a decade: a sudden flash of energy shot off the center of a distant galaxy, bright enough to be visible from 8.5 billion light-years away. With a burst of light equivalent to more than 1,000 trillion suns, the flash was first detected by the Zwicky Transit Facility, an all-sky night-sky survey conducted from the Palomar Observatory in California.

“This Valentine’s Day, we found a baffling source. It was just plain weird!” Igor Andreone of the University of Maryland, lead author of the book One From two papers about the event, he said the edge. “And Strange is good at science. That means it’s something you can learn from.”

Within days, astronomers around the world pointed their telescopes at the flash, observing it in X-rays, radio, and other wavelengths. It was unusually bright and was similar to a gamma-ray burst – a type of bright flash usually detected by gamma-ray or X-ray telescopes. But this was spotted with an optical telescope.

The flash’s enormous brightness led astronomers to conclude that it must have been caused by a star rupture. A star has wandered too close to a supermassive black hole into the heart of a galaxy and is being torn apart by gravitational forces. “It can completely tear the star apart. It literally gets pulled and stretched until it can’t stand together anymore. This is called a tidal disruption event, and astronomers have observed dozens of such events over recent years,” Andreone explained.

What’s unusual about this particular event is that it created a massive outpouring of energy, as material is thrown out of the black hole’s poles at nearly the speed of light. “We don’t know why, but sometimes a very strong jet of material is released when a star is disrupted,” Andreoni said. This jet is thought to be particularly bright because it is pointed directly at Earth, making it appear brighter and visible across a wider part of the electromagnetic spectrum.

To spot exciting transient events like these, astronomers need telescopes that are constantly scanning as much of the sky as possible and that spot any sudden changes in brightness — such as the Zwicky transient facility. But there are thousands of changes in brightness observed each night, so this vast amount of data needs to be refined to discover the most interesting things. Andreoni’s group is sifting through this data to find very fast events in the optical wavelength.

The sudden changes in brightness are likely caused by a supernova explosion or by the merger of two neutron stars. More observations are needed to understand the specific event that triggered the blinking. The supernova, for example, glows over a period of weeks, which is very fast by astronomical standards. But this particular event brightened faster than that, within a few hours or days. Which made it of immediate and urgent importance.

The group reported this flash to the international community, and encouraged researchers who worked with telescopes that operate at other wavelengths such as radio or X-rays to monitor it as well. In total, 21 telescopes contributed data on the event. “When all the pieces of the puzzle were obtained and put together, this picture came out, which was absolutely amazing,” said Andreone. “We didn’t expect to find such a rare source, certainly not in optics.”

Of the stars torn apart by black holes, only about 1 percent appear to produce these powerful jets, but researchers still aren’t quite sure why. When a star is pulled apart and its material is pulled toward the black hole, the energy of that material is converted into light. It is hypothesised that the magnetic fields and spin of the black hole could work together to send material falling off its poles — like a tube of paint squeezed in the middle so that matter flies out at both ends.

“We’re talking about a mass of Earth being pulled apart, twisted, and released at nearly thousands of times the speed of light. It’s a really unique opportunity to study something that would be impossible to reproduce on Earth,” Andreone said.

It was the first time such a jet had been detected in the visible-light portion of the electromagnetic spectrum, also known as the optical wavelength. Previously, jets from around black holes were detected by looking at x-rays, gamma rays, and radio waves.

Both tell astronomers something about the environment around a black hole — that it’s not that dense because it allowed optical light to pass through — and show that looking into the optical scope could be a useful way to spot these extreme events in the future.

The need for telescopes to respond quickly to such events also creates an impetus for greater flexibility in telescope design and planning. Telescopes like Hubble or James Webb are extremely popular, which means that more researchers are applying for time on the telescope than can be accommodated. That is why the observance of time is meticulously planned years in advance and Every last minute of observation time As much as possible. But there is also a need for telescopes that can respond to rare events in a matter of hours or even minutes.

It is difficult to change the direction of a space telescope safely and quickly, so Hubble and the James Webb Space Telescope contribute to this type of search only occasionally. But recently built ground-based telescopes, such as master network or the GROWTH-India Telescopespecialize in scanning the sky for gamma-ray events and taking immediate, independent action to monitor them.

And there is always the option of human-based intervention. Andreone said, “Sometimes you literally have to call people up and say, ‘Hey, could you please point the telescope at this or that coordinate?'” In other cases, researchers are submitting requests through online systems to make observations during available moments. There is growing interest in looking at how telescopes respond to these short, rare, but scientifically important events.

Andreone said that both international collaboration between researchers working with different telescopes and the ability of those telescopes to respond quickly are essential to achieving this breakthrough in observing the black hole. “This was very important for this kind of discovery. If we couldn’t do that with any telescope, we wouldn’t have realized we were sitting on such a big find.”