About 700 million years ago, a small subatomic particle was born into a galaxy, far away, and began its journey across the vast expanses of our universe. That neutrino finally reached the Earth’s South Pole last October, burying the detectors deep under the Antarctic ice. A few months ago, a telescope in California recorded a bright glow emanating from the friction of the same galaxy – evidence of a so-called “tidal disturbance event” (TDE), probably the result of a star passing through a very large black hole.
According to two new articles (here and here) published in the journal Nature Astronomy, the one-time neutrino was probably born from the TDE, which acts as a cosmic particle accelerator near the center of the distant galaxy, spitting out high-energy subatomic. particles as the star’s matter is digested through the black hole. This finding also sheds light on the origin of ultra-high-energy cosmic rays, a question that has amazed astronomers for decades.
“The origin of high-energy cosmic neutrinos is unknown, especially because they are difficult to determine,” said co-author Sjoert van Velzen, a postdoctoral fellow at the University of New York at the time of the discovery. “This result is only the second time that high-energy neutrinos have been returned to their source.”
Neutrinos move very close to the speed of light. John Updike’s 1959 poem, “Cosmic Gall”, pays homage to the two most defining characteristics of neutrinos: they have no charge and physicists have for decades believed that they had no mass (they actually have a small bit mass). Neutrinos are the most subatomic particles in the universe, but very rarely interact with any kind of matter. We are constantly bombarded every second by millions of these tiny particles, but it goes right through us without us even realizing it. That’s why Isaac Asimov calls them ‘ghost particles’.
Those low interactions make neutrinos very difficult to detect, but because they are so light, they can escape unimpeded (and thus largely unchanged) by collisions with other particles. This means that they can provide valuable clues to astronomers about distant systems, further supplemented by what can be learned with telescopes across the electromagnetic spectrum, as well as gravitational waves. Together, these different sources of information are called “multi-messenger” astronomy.
The majority of neutrinos that reach the earth come from our own sun, but every now and then neutrino detectors pick up the rare neutrinos that come from further afield. This is the case with this latest discovery: a neutrino that began its journey in a distant, yet unnamed galaxy in the constellation Delphinus, born from the death throes of a shredded star.
DESY, Science Communication Laboratory
As we reported earlier, it is a popular misconception that black holes act like cosmic vacuum cleaners and sincerely suck up every thing in their environment. In reality, only things that go beyond the horizon of the event – including light – are swallowed up and cannot escape, although black holes are also messy eaters. This means that part of an object’s case is thrown into a powerful jet. If that object is a star, the process of shredding (or ‘spaghettiification’) takes place by the powerful gravitational forces of a black hole outside the event horizon, and part of the star’s original mass is forcibly shot out . This in turn can form a rotating ring of matter (also known as a growth disk) around the black hole that emits powerful X-rays and visible light.
Tide disruption describes the large forces that arise when a small body moves very close to a much larger one, like a star wandering too close to a supermassive black hole. “Gravity gets stronger and stronger the closer you get to something. That means the gravity of the black hole pulls the star’s near side stronger than the star’s other side, leading to a regional effect,” said Robert Stein of DESY . in Germany. “As the star approaches, this stretch becomes more extreme. Eventually it tears the star apart, and then we call it a tidal disturbance event. It’s the same process that leads to tides on Earth, but fortunately the moon will do not pull hard enough to shred the earth. ‘
TDEs are probably fairly common in our universe, though to date only a few have been detected. For example, in 2018, astronomers announce the first direct image of the aftermath of a star torn by a black hole 20 million times more massive than our sun, in some colliding galaxies called Arp 299, about 150 million light-years from the earth off. Last fall, astronomers recorded the last dying moments of a star shredded through a supermassive black hole, which published the discovery in Nature Astronomy.
The glow of this most recent TDE was first detected on April 9, 2019 by the Zwicky Transient Facility (ZTF) in the Mount Palomar Observatory in California, which has noticed more than 30 such events since it came online in 2018. Almost five months later, on October The IceCube neutrino observatory at the South Pole recorded the signal of a highly energetic neutrino coming from the same direction as the TDE. How energetic was it just? Co-author Anna Franckowiak of DESY captured the energy at more than 100 tera-electron volts (TEV), ten times the maximum energy for subatomic particles that can be produced by the Large Hadron Collider.
Ice cube / NSF
The probability of detecting this lone high-energy neutrino was only 1 in every 500. ‘This is the first neutrino linked to an event of tidal disruption, and it brings us valuable evidence,’ Stein said. . “The disruption of tides is not well understood. The detection of the neutrino indicates the existence of a central, powerful engine near the growth disk, which spits out fast particles. And the combined analysis of data from radio, optical and ultraviolet telescopes give us extra proof that the TDE acts as a giant particle accelerator. ‘
This is another example of all the new knowledge that can be gained by combining different data sources to get different perspectives on the same heavenly event. “The combined observations demonstrate the power of astronomy with multiple messages,” said co-author Marek Kowalski of DESY and Humboldt University in Berlin. “Without detecting the tidal disturbance event, the neutrino would be just one of many. And without the neutrino, observing the tidal disturbance event would be just one of many. Only through the combination could we find the accelerator and learn something new about the. processes are. “
As for the future, “We may only see the tip of the iceberg here. In the future, we expect that there will still be many associations between high-energy neutrinos and their sources,” said Francis Halzen of the University of Wisconsin- Madison said. who were not directly involved in the study. “A new generation of telescopes is being built that will provide greater sensitivity to TDEs and other prospective neutrino sources. Even more important is the planned expansion of the IceCube neutrino detector that would increase the number of cosmic neutrino detection at least ten times.”
DOI: Natural Astronomy, 2021. 10.1038 / s41550-020-01295-8
DOI: Nature Astronomy, 2021. 10.1038 / s41550-021-01305-3 (On DOIs).