Ice telescope sees distant galaxy spew ghost particles into space: ‘Milestone, super exciting’

The discovery, published this week in Science, according to experts, is a taste of what awaits us in the promising field of multi-messenger astronomy in the years to come. ‘This is an important step,’ says particle physicist Suzan du Pree of the Nikhef Institute in Amsterdam. “It’s super exciting.”

Astronomers have traditionally studied the electromagnetic radiation of the universe, such as radio waves, visible light and X-rays. But the cosmos sends us much more information in the form of high-energy electrically charged particles, waves gravitational (a kind of “ripples” in empty space) and neutrinos – elusive particles that pass through almost everything in unimaginable numbers. Multi-messenger astronomy attempts to unlock the secrets of the universe by studying all of these “messengers”.

The American IceCube detector in Antarctica targets neutrinos. It consists of more than 5,000 light detectors frozen to great depths in a cubic kilometer of dark arctic ice. Very occasionally, an invading neutrino indirectly causes a faint flash of light. The origin of the neutrino can then be traced with the IceCube.

In 2017, a very high-energy neutrino was attributed to an explosion in a galaxy nearly 4 billion light-years away. Now, for the second time, a cosmic neutrino source has been identified. Only it’s much closer and it continuously spews ghost particles into space.

According to Aart Heijboer, also affiliated with Nikhef, neutrinos offer “a unique view of the most energetic objects in the universe”. This concerns, for example, supermassive black holes at the heart of galaxies. They work like gigantic particle accelerators, but then a million times more powerful than the accelerator at the CERN research institute.

Black holes also produce high-energy gamma rays, but these are often absorbed by cosmic dust. And the electrically charged particles they blow into space are deflected by the magnetic fields of the universe – so you can’t trace their origin. “Neutrinos have no electrical charge and are the ultimate ‘messenger’ particles to study this cosmic particle accelerator,” says Heijboer.

IceCube scientists studied data from 2011 to 2020 and found 79 neutrinos that appear to come from the galaxy M77 (sometimes called the Squid Galaxy). This galaxy is home to a central black hole that is tens of millions of times more massive than the Sun. According to Heijboer, M77 could well become the typical example of cosmic neutrino sources.

“These are just the first observations with an entirely new type of telescope,” he says, “similar to Galileo who first saw Jupiter’s moons in 1610. There’s still a whole neutrino sky to discover.

Heijboer’s colleague Bouke Jung is also confident that many more such sources will be discovered in the future. ‘The European KM3NeT detector, which will have excellent directivity, has a major role to play in this respect,’ he says. KM3NeT is under construction at the bottom of the Mediterranean Sea; through Nikhef, the Netherlands is an important partner in the project.

“There’s still a lot we don’t fully understand about these types of objects and about high-energy neutrino production,” Jung says. “So every new announcement about the discovery of a cosmic neutrino source keeps me on the edge of my seat for years to come.”