Only the second time astronomers have linked a transient particle called a high-energy neutrino to an object outside our galaxy. Using ground and space-based facilities, inclusive NASANeil Gehrels Swift Observatory, tracked the neutrino to black hole tearing apart a star, a rare cataclysmic event called a tidal disruptive event.
“Astrophysicists have long theorized that tidal disruptions could produce high-energy neutrinos, but this is the first time we have actually been able to link them with observational evidence,” said Robert Stein, a doctoral student at the German Electron Synchrotron (DESY) research center in Zeuthen, Germany, and Humboldt University in Berlin. “But it seems that this particular event, called AT2019dsg, did not generate the neutrino when or how we expected. It helps us better understand how these phenomena work.”
The findings, led by Stein, were published in Natural Astronomy.
Watch as a monster black hole tearing apart a star may have launched a ghost particle to Earth. Astronomers have predicted that events of tidal disruption could produce high-energy neutrinos, almost massless particles from outside our galaxy traveling close to the speed of light. One recent event, called AT2019dsg, gives the first proof that this prediction is true, but has challenged scientists ’assumptions about where and when these evasive particles could form during these destructive explosions. Credit: NASA’s Goddard Space Flight Center
Neutrinos are fundamental particles that far exceed all atoms in the universe, but rarely interact with anything else. Astrophysicists are particularly interested in high-energy neutrinos, which have energies up to 1,000 times greater than those produced by the most powerful particle colliders on Earth. They think that the most extreme events in the universe, such as violent galactic explosions, accelerate particles to almost the speed of light. These particles then collide with light or other particles to generate high-energy neutrinos. The first confirmed high-energy neutrino source, announced in 2018, was a kind of active galaxy called a blazar.
Tidal interruptions occur when an unlucky star strays too close to a black hole. Gravitational forces create intense tides that separate the star into a gas stream. The rear part of the stream escapes from the system, while the main part swings back around, surrounding the black hole with a disk of debris. In some cases, the black hole launches fast particles. Scientists have hypothesized that tidal interruptions will produce high-energy neutrinos within such particles. They also expected that the events would produce neutrinos early in their development, with maximum brightness, whatever the production process of the particles.
AT2019dsg was discovered on April 9, 2019, from the Zwicky Transient Facility (ZTF), a robotic camera at Caltech’s Palomar Observatory in Southern California. The event took place more than 690 million light-years away in a galaxy called 2MASX J20570298 + 1412165, located in the constellation Delphinus.
As part of a routine follow-up investigation of tidal interruptions, Stein and his team requested visible, ultraviolet, and X-ray observations with Swift. They also made X-ray measurements using the European Space Agency’s XMM-Newton satellite and radio measurements with facilities including Karl G. Jansky’s Very Large Array from the National Radio Astronomy in Socorro, New Mexico, and the MeerKAT telescope. South African Radio Astronomy Observatory
Peak glow came and went in May. No clear jet appeared. According to theoretical predictions, AT2019dsg looked like a poor neutrino candidate.
Then, on October 1, 2019, the National Science Foundation’s IceCube Neutrino Observatory at the Amundsen-Scott South Pole Station in Antarctica detected a high-energy neutrino called IC191001A and retreated along its trajectory to a location in the sky. About seven hours later, ZTF noticed that this same sky included AT2019dsg. Stein and his team believe there is only one chance in 500 that the tidal disruption is not the source of the neutrino. Because the detection occurred about five months after the event reached peak brightness, it raises questions about when and how these events produce neutrinos.
“Tidal wave events are incredibly rare phenomena, occurring only once every 10,000 to 100,000 years in a large galaxy like ours. Astronomers have only observed a few dozen at this point,” said Swift Chief Investigator S. Bradley Cenko at the Goddard Space Flight NASA Center in Greenbelt, Maryland. “Multi-wavelength measurements of each event help us learn more about them as a class, so AT2019dsg is very interesting even without initial neutrino detection.”
For example, tidal interruptions generate visible and UV light in the outer regions of their hot surface discs. In AT2019dsg, these wavelengths leveled shortly after they peaked. This was unusual because such plateaus typically appear only after a few years. Researchers suspect the galaxy’s monstrous black hole, with a mass estimated to be 30 million times that of the Sun, could have forced the stellar debris to enter a disk faster than it could have around a less massive black hole.
AT2019dsg is one of only a few known X-ray broadcast tidal interruptions. Scientists believe that the X-rays come from either the inner part of the overhead disk, close to the black hole, or from high-speed particles. The X-rays of the explosion faded at an unprecedented 98% for 160 days. Stein’s team sees no clear evidence indicating the presence of jets and instead suggests a rapid cooling in the disk most likely explains the abrupt drop in X-rays.
Not everyone agrees with this analysis. Another explanation, written by Walter Winter of DESY and Cecilia Lunardini, a professor at Arizona State University in Tempe, proposes that the emission came from a jet that was quickly obscured by a cloud of debris. The researchers published their alternative interpretation in the same issue of Natural Astronomy.
Astronomers think that radio emission in these phenomena comes from the black hole accelerating particles, whether in jets or more moderate outflows. Stein’s team thinks AT2019dsg falls into this latter category. The scientists also discovered that the radio emission lasted steadily for months and did not disappear along with the visible and UV light, as previously assumed.
The detection of neutrinos, combined with the measured wave measurements, prompted Stein and his colleagues to rethink how tidal disruptions could produce high-energy neutrinos.
The radio emission shows that particle acceleration occurs even without clear, powerful jets and can work well after peak UV and visible brightness. Stein and his colleagues suggest that these accelerated particles could produce neutrinos in three distinct regions of tidal disruption: in the outer disk by collisions with UV light, in the inner disk by collisions with X-rays, and in the moderate outflow of particles by collisions. with other items.
Stein’s team suggests that the neutrino from AT2019dsg probably originated from the UV-bright outer part of the disk, based on the fact that the energy of the particle was more than 10 times greater than achievable by particle colliders.
“We predicted that neutrinos and tidal interruptions could be related, and seeing that for the first time in the data is just very exciting,” said co-author Sjoert van Velzen, an assistant professor at Leiden University in the Netherlands. “This is another example of the power of multi-message astronomy, using a combination of light, particles and space-time waves to learn more about the cosmos. When I was a graduate student, it was often predicted that this new era of astronomy would come, but now actually being a part of it is very rewarding. “
Goddard manages the Swift mission in collaboration with Penn State, the Los Alamos National Laboratory in New Mexico, and Northrop Grumman Innovation Systems in Dulles, Virginia. Other partners include the University of Leicester and Mullard Space Science Laboratory in the United Kingdom, Brera Observatory, and the Italian Space Agency in Italy.
For more on this research:
“Tidal disruptive event coinciding with high energy neutrino” by Robert Stein, Sjoert van Velzen, Marek Kowalski, Anna Franckowiak, Suvi Gezari, James CA Miller-Jones, Sara Frederick, Itai Sfaradi, Michael F. Bietenholz, Assaf Horesh, Rob Fender, Simone Garrappa, Tomás Ahumada, Igor Andreoni, Justin Belicki, Eric C. Bellm, Markus Böttcher, Valery Brinnel, Rick Burruss, S. Bradley Cenko, Michael W. Coughlin, Virginia Cunningham, Andrew Drake, Glennys R. Farrar, Michael Feeney, Ryan J. Foley, Avishay Gal-Yam, V. Zach Golkhou, Ariel Goobar, Matthew J. Graham, Erica Hammerstein, George Helou, Tiara Hung, Mansi M. Kasliwal, Charles D. Kilpatrick, Albert KH Kong, Thomas Kupfer, Russ R. Laher, Ashish A. Mahabal, Frank J. Masci, Jannis Necker, Jakob Nordin, Daniel A. Perley, Mickael Rigault, Simeon Reusch, Hector Rodriguez, César Rojas-Bravo, Ben Rusholme, David L. Shupe, Leo P. Singer, Jesper Sollerman, Maayane T. Soumagnac, Daniel Stern, Kirsty Taggart, Jakob van Santen, Charlotte Ward, Patri ck Woudt and Yuhan Yao, 22 February 2021, Natural Astronomy.
DOI: 10.1038 / s41550-020-01295-8
“A concordant scenario for the observed neutrino of a tidal disruptive event” by Walter Winter and Cecilia Lunardini, 22 February 2021, Natural Astronomy.
DOI: 10.1038 / s41550-021-01305-3