A black hole tore apart a star and brought together astronomers from around the world

It was an event not seen in over a decade: a sudden burst of energy launched from the center of a distant galaxy, bright enough to be visible 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 Transient Facility, a survey of the entire night sky conducted from the Palomar Observatory in California.

“On Valentine’s Day this year, we found a source that was confusing. It was just weird!” Igor Andreoni of the University of Maryland, lead author of one of two papers on the event, said The edge. “And weird is good at science. That means it’s something you can learn from.

Within days, astronomers around the world turned their telescopes to the flash, observing it in X-rays, radio and other wavelengths. It was extraordinarily bright and resembled a gamma-ray burst – a type of bright flash usually detected by gamma-ray or x-ray telescopes. But this one had been spotted by an optical telescope.

The enormous brightness of the lightning led astronomers to conclude that it must have been caused by the splitting of a star. A star had come too close to the supermassive black hole at the heart of a galaxy and been shredded by gravitational forces. “It can completely rip the star apart. It’s literally pulled and stretched until it can’t hold together anymore,” Andreoni explained. This is called a tidal disturbance event, and the Astronomers have spotted dozens of these events over the past few years.

What’s unusual about this particular event is that it created a huge jet of energy, with matter ejected from the poles of the black hole at near the speed of light. “We don’t know why, but sometimes a very strong jet of material is launched when the star is disturbed,” Andreoni said. This jet is thought to have been particularly bright because it is aimed directly at Earth, making it both brighter and visible over a wider part of the electromagnetic spectrum.

To spot dramatic transient events like these, astronomers need telescopes that continuously scan as much of the sky as possible and report any sudden changes in brightness, like the Zwicky Transient Facility. But there are thousands of changes in brightness observed each night, so this mountain of data must be honed to unearth the most interesting objects. Andreoni’s group is working to sift through this data to find very fast events in the optical wavelength.

Sudden changes in brightness could potentially be caused by a supernova or by the merger of two neutron stars. Further observations are needed to understand the specific event that triggered the flash. A supernova, for example, lights up over a period of weeks, which is extremely fast by astronomical standards. But this particular event cleared up even faster than that, within hours or days. This made it an immediate and pressing interest.

The group reported this flash to the international community, encouraging researchers who worked with telescopes operating in other wavelengths such as radio or X-rays to observe it as well. A total of 21 telescopes provided data on the event. “When all the pieces of the puzzle were acquired and put together, this picture appeared, which was just amazing,” Andreoni said. “We did not expect to find such a rare source, and certainly not in optics.”

Of the stars torn apart by black holes, only about 1% appear to produce these powerful jets, but researchers still don’t know exactly why. As the star is pulled apart and its matter is pulled towards the black hole, the energy of that matter is converted into light. It is theorized that the magnetic fields and the black hole’s rotation could act together to send matter squirting out of its poles – like a tube of paint pressed down the middle until matter flies out of either end.

“We are talking about thousands of times the mass of the Earth being separated, spun and launched at near the speed of light. It’s a really unique opportunity to study something that’s impossible to replicate on Earth,” Andreoni 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 around black holes have been detected by looking at X-rays, gamma rays, and radio waves.

This both tells astronomers something about the environment around the black hole – that it’s not so dense because it lets optical light through – and shows that looking into the optical range could be a useful way to spot these extreme events in the future.

The need for telescopes to react quickly to such events also creates an impetus for greater flexibility in telescope design and planning. Telescopes like Hubble or James Webb are vastly oversubscribed, meaning many more researchers request time on the telescope than can be accommodated. This is why observing time is meticulously planned years in advance and every last minute of observing is filled in as much as possible. But there is also a need for telescopes capable of responding to rare events within hours or even minutes.

Changing the direction of a space telescope quickly and safely is difficult, so Hubble and the James Webb Space Telescope only occasionally contribute to this type of research. But recently built ground-based telescopes, like the MASTER array or the GROWTH-India telescope, specialize in scanning the sky for gamma-ray events and moving immediately and autonomously to observe them.

And there is always the option of human intervention. “Sometimes you literally have to call people up and say, ‘Hey, can you please point the telescope at this or these coordinates? “Said Andreoni. In other cases, researchers submit requests through online systems to make observations during available moments. There is growing interest in how telescopes can respond to these events. brief and rare but scientifically important.

International cooperation between researchers working with different telescopes and the ability of these telescopes to respond quickly were key to making this breakthrough in black hole observation, Andreoni said. “It was extremely important for this kind of discovery. If we couldn’t do it with any telescope, we wouldn’t have realized we were sitting on such a great discovery.