A mysterious object is being dragged into the supermassive black hole at
the Milky Way's center
Astronomers think the object, X7, might be debris cloud from a stellar collision

Date:
February 24, 2023
Source:
University of California - Los Angeles
Summary:
An object near the supermassive black hole at the center of the
Milky Way galaxy has drawn the interest of scientists because it
has evolved dramatically in a relatively short time. A new study
suggests that the object, called X7, could be a cloud of dust and
gas that was created when two stars collided. The researchers
believe it will eventually be drawn toward the black hole and
will disintegrate.


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FULL STORY ==========================================================================
For two decades, scientists have observed an elongated object named
X7 near the supermassive black hole at the center of the Milky Way and
wondered what it was. Was it pulled off a larger structure nearby? Was
its unusual form the result of stellar winds or was it shaped by jets
of particles from the black hole?

==========================================================================
Now, having examined the evolution of X7 using 20 years of data gathered
by the Galactic Center Orbit Inintiative, astronomers from the UCLA
Galactic Center Group and the Keck Observatory propose that it could be a
cloud of dust and gas that was ejected during the collision of two stars.

Over time, they report, X7 has stretched, and it is being pulled apart
as the black hole drags it closer, exerting its tidal force upon the
cloud. They expect that within the next few decades, X7 will disintegrate
and the gas and dust of which it is composed will eventually be drawn
toward the black hole, which is called Sagittarius A*, or Sgr A*.

The study is published in The Astrophysical Journal.

"No other object in this region has shown such an extreme evolution," said
Anna Ciurlo, a UCLA assistant researcher and the paper's lead author. "It started off comet-shaped and people thought maybe it got that shape from stellar winds or jets of particles from the black hole. But as we followed
it for 20 years we saw it becoming more elongated. Something must have
put this cloud on its particular path with its particular orientation."
X7 has a mass of about 50 Earths and is on an orbital path around Sgr A*
that would take 170 years to complete.

But that might never happen. Based on its trajectory, the team estimates
that X7 will make its closest approach to Sgr A* around the year 2036,
and then likely spiral toward Sgr A* and disappear.

"We anticipate the strong tidal forces exerted by the galactic black
hole will ultimately tear X7 apart before it completes even one orbit,"
said co-author Mark Morris, UCLA professor of physics and astronomy.

Tidal forces are the gravitational pull that cause an object approaching
a black hole to stretch; the side of the object closest to the black
hole is pulled much more strongly than the opposite end.

X7 shows some of the same properties as the other strange dusty objects orbiting Sgr A*. Those so-called G objects look like gas but behave
like stars.

But X7's shape and velocity have changed more dramatically than G objects' have. As it accelerates toward the black hole, X7 is moving rapidly,
clocking in at speeds of up to around 700 miles per second.

"It's exciting to see significant changes of X7's shape and dynamics in
such great detail over a relatively short time scale as the gravitational forces of the supermassive black hole at the center of the Milky Way
influences this object," Randy Campbell, a co-author of the paper and
the science operations lead at the Keck Observatory, said in a statement.

Although X7's origin is still the subject of debate, the finding suggests
that it arose after two stars collided.

"One possibility is that X7's gas and dust were ejected at the moment
when two stars merged," Ciurlo said. "In this process, the merged star
is hidden inside a shell of dust and gas, which might fit the description
of the G objects. And the ejected gas perhaps produced X7-like objects."
The merger of two stars is very common, especially when they are near
black holes, Ciurlo said.

"This is a very messy process: The stars circle each other, get closer,
merge, and the new star is hidden within a cloud of dust and gas," she
said. "X7 could be the dust and gas ejected from a merged star that's
still out there somewhere." The findings are the first estimate of
X7's mildly elliptical orbit and the most robust analysis to date of the remarkable changes to its appearance, shape and behavior. The research
team will continue to use the Keck Observatory to monitor X7's dramatic
changes as the power of the black hole's gravity yanks it apart.

"It's a privilege to be able to study the extreme environment at the
center of our galaxy," Campbell said in the statement. "This study can
only be done using Keck's superb capabilities, and performed at the very special and revered Maunakea, with honor and respect to the mauna."
* RELATED_TOPICS
o Space_&_Time
# Black_Holes # Galaxies # Stars # Astronomy #
Astrophysics # Nebulae # Asteroids,_Comets_and_Meteors
# Cosmology
* RELATED_TERMS
o Spitzer_space_telescope o Galaxy o Black_hole o
Magellanic_Clouds o Satellite o Holographic_Universe o
Planetary_nebula o Supernova

========================================================================== Story Source: Materials provided by
University_of_California_-_Los_Angeles. Original written by Holly
Ober. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Anna Ciurlo, Randall D. Campbell, Mark R. Morris, Tuan Do, Andrea M.

Ghez, Eric E. Becklin, Rory O. Bentley, Devin S. Chu, Abhimat
K. Gautam, Yash A. Gursahani, Aure'lien Hees, Kelly Kosmo O'Neil,
Jessica R. Lu, Gregory D. Martinez, Smadar Naoz, Shoko Sakai,
Rainer Scho"del. The Swansong of the Galactic Center Source X7:
An Extreme Example of Tidal Evolution near the Supermassive
Black Hole. The Astrophysical Journal, 2023; 944 (2): 136 DOI:
10.3847/1538-4357/acb344 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/02/230224135122.htm

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