February 23, 2021, 8:17 a.m.
Research team finds first neutrino from a ripped star. A press release from the German Electron Synchrotron DESY – a research center of the Helmholtz Association.
  Smoking gun: Around half of the debris of the torn star was thrown straight back into space, while the rest formed a brightly shining accretion disk around the central supermassive black hole.  The best explanation for the observations is provided by a model in which energetic streams of matter shoot up and down out of the system. A powerful, central drive near the accretion disk hurls fast subatomic particles into space. (Bild: DESY, Science Communication Lab) |
February 22, 2021 – A ghostly elementary particle from a ripped star has put an international research team on the trail of a gigantic cosmic particle accelerator:
The so-called neutrino could be traced back to a supermassive black hole in a distant galaxy, to which the star came too close and then from whose colossal gravity had been destroyed. It is the first particle that could be linked to such a tidal disaster (?? Tidal Disruption Event ??).
The observation proves that these little-understood cosmic catastrophes could drive high-energy particle accelerators, as the team led by DESY researcher Robert Stein in the journal ?? Nature Astronomy ?? reported.
The work also shows the potential of so-called multi-messenger astronomy, i.e. the observation of the cosmos with the help of various messengers such as photons (light particles) and neutrinos.
The neutrino began its journey around 700 million years ago, around the time when the first animals evolved on earth. That’s how long the flight from the nameless galaxy with the catalog number 2MASX J20570298 + 1412165 in the constellation Dolphin took.
The researchers estimate the mass of the gigantic black hole in the center of the galaxy to be that of around 30 million suns. ?? Gravity gets stronger and stronger the closer you get to an object. This also means that the black hole pulled more strongly on the front of the star a little closer than on its back a little further away, ”explains Stein.
The difference that stretched the star is called the tidal force, and the closer the star gets to the black hole, the more extreme it is elongated. At some point it will tear the star apart, then we have a tidal disaster. It’s basically the same process that causes ebb and flow on earth, but luckily for us, the moon doesn’t pull the earth hard enough to tear it apart.
Around half of the stellar matter in the distant galaxy was hurled straight into space after the tidal disaster, the rest was collected on a swirling disk around the black hole. This so-called accretion disk is similar to the vortex over the drain of a bathtub. Before the matter disappears into the black hole, never to be seen again, it gets hotter and hotter and finally glows brightly.
The Zwicky Transient Facility (ZTF) observatory on Mount Palomar, California, first discovered this glow on April 9, 2019.
Half a year later, on October 1st, 2019, the underground neutrino telescope IceCube registered an extremely high-energy neutrino in the eternal ice of the South Pole from the direction of the tidal disaster. ??
The particle had rushed into the Antarctic ice with a remarkable energy of more than 100 tera electron volts ??, reports DESY co-author Anna Franckowiak, who now works as a professor at the University of Bochum. For comparison: This is at least ten times the particle energy that the largest particle accelerator on earth can achieve, the Large Hadron Collider at the European nuclear research center CERN near Geneva.
Extreme lightweights
The extremely lightweight neutrinos almost never interact and fly effortlessly through walls and even entire planets or stars without leaving a trace. Hence they are also known as ghost particles, and the detection of a single high-energy neutrino is a remarkable observation.
The evaluation only shows a probability of one in 500 that this particular neutrino came only by chance from the direction of the tidal disaster.
The observation called on more teams to investigate the event with a variety of instruments across the electromagnetic spectrum, from radio waves to x-rays.
“It’s the first neutrino from a tidal disaster, and it gives us valuable clues,” Stein explains. ?? Tidal disasters are so far poorly understood.
The neutrino discovery indicates the existence of a central, powerful machine near the accretion disk that spits out fast particles. And the combined analysis of the data from the radio, optical and ultraviolet telescopes also shows that tidal disasters can function as gigantic particle accelerators.
 Heart of darkness: View of the accretion disk around the supermassive black hole with an energetic flow of matter that shoots upwards away from the disk.
The extreme mass of the black hole bends space-time in such a way that an image of the far side becomes visible above and below the black hole. |
The observations can best be explained with a model, as the head of theoretical astroparticle physics at DESY, Walter Winter, and his colleague Cecilia Lunardini from Arizona State University did in a separate paper in the same issue of ?? Nature Astronomy ?? present. In the process, high-energy flows of matter are formed that shoot up and down out of the system. “
The neutrino appeared relatively late, six months after the black hole’s star feast began,” explains Winter. “Our model explains this timing in a natural way.”
The cosmic accelerator spits out different types of particles, but apart from neutrinos and photons these are all electrically charged and are therefore deflected by intergalactic magnetic fields on their journey through space. Only the electrically neutral neutrinos can, like light (photons), travel in a straight line from the source to the earth and can be traced back.
The y are therefore valuable messengers from such systems.
??
The combined observations demonstrate the strength of multi-messenger astronomy ??, emphasizes co-author Marek Kowalski, head of neutrino astronomy at DESY and professor at the Humboldt University in Berlin. Without the evidence of the tidal disaster, the neutrino would be just one of many, and without the neutrino, the observation of the tidal disaster would be just one of many. Only by combining the two were we able to track down the cosmic particle accelerator and learn something about the processes inside it.
The connection between the high-energy neutrino and the tidal catastrophe was tracked down by a computer program called AMPEL, which was specially developed at DESY for the comparison of ZTF and IceCube observations.
Tip of the iceberg?
The Zwicky Transient Facility is designed to observe hundreds of thousands of stars and galaxies in a single shot and to search the night sky particularly quickly. Thanks to its large field of view, the ZTF’s 1.3-meter Samuel Oschin telescope can completely observe the entire night sky in just three nights and thus detect significantly more objects that suddenly light up or fluctuate in brightness than all previous optical surveys. ?? Since the investigations began in 2018, we have detected more than 30 tidal disasters, more than doubling the number of known such phenomena ,? says co-author Sjoert van Velzen from the Leiden Observatory in the Netherlands. When we found out that the second brightest tidal disaster we’ve observed is also the source of a high-energy neutrino registered by IceCube, we were amazed!
?? We may only see the tip of the iceberg here, in the future we expect many more such connections between high-energy neutrinos and their sources ??, emphasizes IceCube chief scientist Francis Halzen, professor at the University of Wisconsin-Madison, who is not involved in this work was. A new generation of telescopes is being built that will offer greater sensitivity to tidal disasters and other suspected neutrino sources. Even more important is the planned expansion of the IceCube neutrino detector, which should increase the number of observed cosmic neutrinos at least tenfold.
The tidal disaster is only the second source that could be assigned to a cosmic neutrino. In 2018, a multi-messenger observation campaign identified the active galaxy with catalog number TXS 0506 + 056 as the source of a high-energy neutrino that was recorded by IceCube in 2017.
The IceCube Neutrino Observatory is a facility of the US National Research Foundation NSF at the Amundsen-Scott South Pole Station of the US Antarctic Program. In addition to IceCube and the Zwicky Transient Facility, the instruments have Spectral Energy Distribution Machine (SEDM), Palomar 200-inch Hale Telescope (P200), Liverpool Telescope (LT), NASA’s Neil Gehrels Swift Observatory, Lowell Discovery Telescope, Lick Observatory Shane Telescope, Keck Telescope, ESA’s X-ray Multi-Mirror Mission (XMM-Newton), Karl G. Jansky Very Large Array (VLA), AMI Large Array (AMI-LA), MeerKAT and NASA’s Fermi Large Area Telescope (Fermi-LAT) contributed to the study.
Original work:
A tidal disruption event coincident with a high-energy neutrino; Robert Stein, Sjoert van Velzen, Marek Kowalski, et al.; Nature Astronomy, 2021,
DOI: 10.1038 / s41550-020-01295-8
A concordance scenario for the observed neutrino from a tidal discruption event; Walter Winter and Cecilia Lunardini; Nature Astronomy, 2021,
DOI: 10.1038 / s41550-021-01305-3
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Ghost particle reveals cosmic accelerator
