Credits: NASA/CXC/Univ of
Michigan/J. Miller et al.; Illustration: NASA/CXC/M.Weiss
Astronomers have made a thorough
forensic study of a star that was torn apart when it ventured too close to a
giant black hole and then had its insides tossed out into space.
NASA’s Chandra X-ray Observatory
and ESA’s XMM-Newton studied the amount of nitrogen and carbon near a black
hole known to have torn apart a star. Astronomers think these elements were
created inside the star before it was ripped apart as it neared the black hole.
“We are seeing the guts of what
used to be a star,” said Jon Miller of the University of Michigan who led the
study. “The elements left behind are clues we can follow to figure out what
sort of star met its demise.”
Astronomers have found many
examples of “tidal disruption
events” in recent
years, where the gravitational forces from a massive black hole destroy a star.
This causes a flare, often seen in optical and ultraviolet light and X-rays, as
the star’s debris is heated up. This event, called ASASSN-14li, stands out for
several reasons.
At the time of discovery in
November 2014 it was the closest tidal disruption to Earth (290 million
light-years) discovered in about a decade. Because of this proximity,
ASASSN-14li has provided an extraordinary level of detail about the destroyed
star. Miller’s team applied new theoretical models to make improved estimates,
compared to previous work, of the amount of nitrogen and carbon around the
black hole.
“These X-ray telescopes can be used
as forensic tools in space,” said co-author Brenna Mockler of Carnegie
Observatories and the University of California, Los Angeles. “The relative
amount of nitrogen to carbon that we found points to material from the interior
of a doomed star weighing about three times the mass of the Sun.”
The star in ASASSN-14li is
therefore one of the most massive – and perhaps the most massive – that
astronomers have seen ripped apart by a black hole to date.
“ASASSN-14li is exciting because
one of the hardest things with tidal disruptions is being able to measure the
mass of the unlucky star, as we have done here,” said co-author Enrico
Ramirez-Ruiz of the University of California, Santa Cruz. “Observing the
destruction of a massive star by a supermassive black hole is spellbinding
because more massive stars are expected to be significantly less common than
lower-mass stars.”
Earlier this year, another team of
astronomers reported the “Scary Barbie” event where they estimated a star with
about 14 times the mass of the Sun was destroyed by a black hole. However, this
has not yet been confirmed as a tidal disruption, with the estimate of the
star’s mass mainly based on the brightness of the flare, not on a detailed
analysis of material around the black hole as with ASASSN-14li.
Another exciting aspect of the
ASASSN-14li result is what it means for future studies. Astronomers have seen
moderately massive stars like ASASSN-14li’s in the star cluster that contains
the supermassive black hole in the center of our galaxy. Therefore, the ability
to estimate stellar masses of tidally disrupted stars potentially gives
astronomers a way to identify the presence of star clusters around supermassive
black holes in more distant galaxies.
Until this study there was a strong
possibility that the elements observed in X-rays might have come from gas
released in previous eruptions from the supermassive black hole. The pattern of
elements analyzed here, however, appears to have come from a single star.
Previous work published in 2017 by
Chenwie Yang from the University of Science and Technology in Hefei, China,
used ultraviolet data from NASA’s Hubble Space Telescope to show that there is
enhanced nitrogen compared to carbon in ASASSN-14li, but by a smaller amount
than Miller’s team found using X-ray data. Those authors found the star to be
only more massive than 0.6 times that of the Sun.
The new paper was published in the
August 20, 2023 issue of The Astrophysical Journal Letters and is available here. The other authors of the paper,
in addition to Miller, Mockler, and Ramirez-Ruiz, are Paul Draghis (University
of Michigan), Jeremy Drake (Center for Astrophysics | Harvard &
Smithsonian), John Raymond (CfA), Mark Reynolds (University of Michigan), Xin
Xiang (University of Michigan), Sol Bin Yun (University of Michigan), and
Abderahmen Zoghbi (University of Maryland).
NASA's Marshall Space Flight Center
manages the Chandra program. The Smithsonian Astrophysical Observatory's
Chandra X-ray Center controls science operations from Cambridge, Massachusetts,
and flight operations from Burlington, Massachusetts.
Read more from NASA's Chandra
X-ray Observatory.
For more Chandra images, multimedia and related materials, visit: http://www.nasa.gov/chandra
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