A single high-energy neutrino could have supplied astrophysicists with telltale details about the tidal disruption of a star by a supermassive black gap some 750 million light-years away.
An artist’s impression of the tidal disruption occasion AT2019dsg, which could have produced high-energy neutrinos.
DESY / Science Communication Lab
The Neutrino and the Star-nabbing Black Gap
The sub-surface IceCube Neutrino Observatory in Antarctica detected the neutrino on October 1, 2019. The tiny, ghostlike particle was packing a punch of about 200 tera-electronvolts (15 occasions extra energetic than what could be achieved in CERN’s Massive Hadron Collider). It got here from the course of the small constellation Delphinus. Whereas IceCube can’t exactly pinpoint the particle’s origin, the detector can slender down the supply to inside an space of roughly 10 sq. levels on the sky.
“Inside seven hours, we had been observing the realm with the Zwicky Transient Facility (ZTF),” says Robert Stein (DESY, Germany). ZTF is a wide-field sky survey using the refurbished Samuel Oschin 1.2-meter Schmidt telescope at Palomar Observatory.
Earlier than lengthy, Stein and his colleagues discovered the still-fading glow of a tidal disruption occasion (TDE) that had been detected on April 9, 2019, additionally by ZTF. These occasions happen when stars enterprise too near a supermassive black gap; they flare as they’re torn to shreds within the robust gravitational subject.
“Clearly, this was probably the most promising candidate” for the neutrino’s origin,” Stein says. Theorists had already advised that TDEs would possibly produce high-energy neutrinos, probably in relativistic jets of plasma that shoot out from close to the black gap.
The April ninth TDE, catalogued as AT2019dsg, was a fairly particular beast. The optical/ultraviolet outburst, which peaked in Might, occurred within the nucleus of a comparatively luminous galaxy, suggesting star had been destroyed by the tidal forces of an enormous central black gap, most likely weighing in at some 30 million photo voltaic lots.
“I’m excited and joyful that individuals are discovering this potential affiliation,” feedback Dorothea Samtleben (Dutch Nationwide Institute for Subatomic Physics, Amsterdam), who was not concerned with the discover.
Nevertheless, she warns that it’s not a closed case — because the researchers observe, there’s nonetheless a zero.5% probability that the neutrino and the TDE don’t have anything to do with one another.
In keeping with Sjoert van Velzen (Leiden Observatory, The Netherlands), who led the crew that originally found the tidal disruption occasion, the 18th-magnitude supply began to provide brilliant however quickly fading X-rays after 5 weeks, whereas emitting growing quantities of radio waves for a lot of months after the preliminary explosion.
The radio waves end result from high-energy charged particles spiraling round magnetic subject traces. Apparently, the TDE is an environment friendly particle accelerator. “The radio information inform us that the particle acceleration course of have to be fairly steady,” says Stein. “It’s not like an explosive engine,” provides van Velzen, “however extra like a locomotive.”
This may clarify how a TDE can produce a high-energy neutrino virtually half a yr after the beginning of the occasion. To create a neutrino, a high-energy proton should slam into one other proton or right into a photon. If particles are accelerated over an extended time period, there’s ample alternative for neutrino manufacturing at a late stage.
How Do Black Holes Make Neutrinos?
Within the February 22nd difficulty of Nature Astronomy, Stein, van Velzen, and 56 coauthors describe a “multi-zone” state of affairs for the TDE. In keeping with this state of affairs, the extraordinarily scorching internal a part of the transient accretion disk that kinds from the torn-apart star’s stays generates X-rays near the black gap’s occasion horizon. In the meantime, at bigger distances, 40,000-degree gasoline, additionally from the star, emits ultraviolet radiation. Radio waves are produced even additional out, in a broad outflow. Curiously, the researchers didn’t discover any proof for relativistic jets.
Of their view, shock waves or magnetic fields speed up the protons which might be near the central black gap. The energized protons then collide with the plentiful ultraviolet photons farther out to create high-energy neutrinos that escape the system. One of many neutrinos touring in Earth’s course occurred to get caught within the IceCube detector some 750 million years later.
IceCube Observatory throughout winter
Raffaela Busse / IceCube / NSF
Writing in the identical difficulty of Nature Astronomy, Walter Winter (DESY) and Cecilia Lunardini (Arizona State College) counsel a unique state of affairs, partly primarily based on the truth that the TDE’s X-ray emission light so quickly. Key to their state of affairs is the concept the TDE did produce jets of charged particles rushing away from the black gap.
“The thought is that the [UV-producing] outflow expands and begins to trigger a partial obscuration of the X-rays emitted by the accretion disk,” explains Lunardini. “The X-ray photons which might be blocked by the outflow are re-emitted in all instructions, and a few of them find yourself contained in the jets.” When high-velocity protons within the jets collide with these X-ray photons, they produce high-energy neutrinos.
A lot stays unsure, although. “With just one neutrino noticed from a TDE, you can’t actually draw agency conclusions, and the info stay open to interpretation,” admits Lunardini. Stein warns that not everybody agrees on why the X-rays disappeared so shortly. As for the existence of relativistic jets, there’s no corroborating gamma-ray proof.
Up to now, the Zwicky Transient Facility has discovered a pair dozens of tidal disruption occasions, however a few of their options elude clarification. “Neutrinos can assist to study extra about TDEs and their variety sooner or later,” Lunardini notes.
“An important conclusion,” says Stein, “is that TDEs can speed up particles for such a very long time,” as evidenced each by the radio observations and by the late-time manufacturing of the high-energy neutrino.
This artist’s impression exhibits a part of the KM3NET neutrino detector, to be constructed within the Mediterranean Sea. It is to not scale — whereas the detector items are simply 30 cm throughout, they’re going to be unfold throughout cubic kilometers beneath the ocean.
Samtleben, who’s concerned with the KM3NeT neutrino detector that’s being constructed within the Mediterranean Sea, says she appears ahead to a extra strong hyperlink between TDEs and high-energy neutrinos. Each KM3NeT and the upcoming improve of IceCube may present extra examples with higher pointing accuracy.
Different neutrino detectors will proceed to play a job, too. Already, scientists have reported a second doable TDE-neutrino affiliation, primarily based on a neutrino detected in Might 2020, she says.