NASA telescopes witnessed a gigantic black hole ripping apart a nearby star. It was the fifth-closest black hole to destroy a star.

Astronomers observed a sharp increase in high-energy X-ray photons near the black hole after the star was completely torn. This indicated that as the star material was dragged toward its death, it produced a heated corona above the black hole.

According to a new Astrophysical Journal study, the event’s proximity gave NASA’s NuSTAR (Nuclear Spectroscopic Telescopic Array) satellite, the most sensitive space telescope capable of observing these wavelengths, an unprecedented view of the corona’s formation and evolution.

A black hole eating a wandering star may help scientists understand more sophisticated black hole-feeding practices.

The work shows how a black hole’s tidal disruption event, which destroys a star, may be used to study what happens to the material before it’s devoured.

Most black holes astronomers can investigate are ringed by billion-mile-wide disks of hot gas that have collected over millennia. These disks can outshine galaxies. A single star being torn apart and consumed stands apparent even around these luminous objects, especially around less active black holes. The process usually takes weeks or months.

Astronomers may study how the black hole’s gravity manipulates the material around it, creating magnificent light shows and novel physical features, thanks to tidal disruption events’ observability and brief duration.

Study co-author Suvi Gezari, an astronomer at the Space Telescope Science Institute in Baltimore, called tidal disruption occurrences a cosmic laboratory. They show us a galaxy’s huge black hole’s real-time feeding.

Unexpected Sign

The latest study focuses on AT2021ehb, an event in a galaxy with a core black hole 10 million times the mass of our Sun (roughly the difference between a bowling ball and the Titanic). The side of the star nearer the black hole was tugged harder than the distant side, stretching it apart and leaving a long noodle of heated gas.

Scientists believe gas collides with itself when swirled around a black hole. Shock waves and gas outflows produce visible light and wavelengths like ultraviolet and X-rays. The material settles into a disk spinning around the black hole, generating low-energy X-rays. This happened in 100 days for AT2021ehb.

The Zwicky Transient Facility (ZTF) at Palomar Observatory in Southern California discovered the event on March 1, 2021. NASA’s Neil Gehrels Swift Observatory and Neutron star Interior Composition Explorer (NICER) telescope (which observes longer X-ray wavelengths) investigated it.

NASA’s NuSTAR began observing the system 300 days after the explosion. Since coronae generally occur with jets of gas flowing in opposite directions from a black hole, scientists were surprised when NuSTAR spotted a corona, a cloud of hot plasma or gas atoms without electrons. The AT2021ehb tidal event had no jets, making the corona detection unexpected. Coronae release the highest-energy X-rays of any black hole, but scientists don’t know where the plasma comes from or how it heats up.

“We’ve never seen a tidal disruption event with X-ray emission like this without a jet, and that’s really spectacular because it means we can potentially disentangle what causes jets and what causes coronae,” said Yuhan Yao, a graduate student at Caltech in Pasadena, California, and lead author of the new study. “Our observations of AT2021ehb agree that magnetic fields play a role in corona formation, and we want to know what’s causing that magnetic field to get so strong.”

Yao is also coordinating a ZTF-identified tidal disruption event search and Swift, NICER, and NuSTAR observation effort. Each observation can provide fresh insights or corroborate AT2021ehb and other tidal disruption events. Yao added, “We want to find as many.”

Mission Details

NuSTAR, a Small Explorer mission directed by Caltech and administered by NASA’s Jet Propulsion Laboratory in Southern California for the Science Mission Directorate in Washington, was designed in conjunction with the Danish Technical University and the Italian Space Agency (ASI). Dulles-based Orbital Sciences Corp. developed the spacecraft. NuSTAR’s mission operations center is at UC Berkeley, while the official data repository is at NASA’s High Energy Astrophysics Science repository Research Center at Goddard Space Flight Center. ASI provides the mission’s ground station and mirror data archive. Caltech runs NASA’s JPL.

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