Astronomers have spotted the farthest galaxy ever

Date:
April 7, 2022
Source:
Harvard-Smithsonian Center for Astrophysics
Summary:
An international team of astronomers has spotted the most distant
astronomical object ever: a galaxy. Shining only ~300 million
years after the Big Bang, it may be home to the oldest stars in
the universe, or a supermassive black hole.



FULL STORY ==========================================================================
An international team of astronomers, including researchers at the Center
for Astrophysics | Harvard & Smithsonian, has spotted the most distant astronomical object ever: a galaxy.


========================================================================== Named HD1, the galaxy candidate is some 13.5 billion light-years away and
is described Thursday in the Astrophysical Journal. In an accompanying
paper published in the Monthly Notices of the Royal Astronomical Society Letters, scientists have begun to speculate exactly what the galaxy is.

The team proposes two ideas: HD1 may be forming stars at an
astounding rate and is possibly even home to Population III stars,
the universe's very first stars -- which, until now, have never been
observed. Alternatively, HD1 may contain a supermassive black hole about
100 million times the mass of our Sun.

"Answering questions about the nature of a source so far away can
be challenging," says Fabio Pacucci, lead author of the MNRAS study,
co-author in the discovery paper on ApJ, and an astronomer at the Center
for Astrophysics.

"It's like guessing the nationality of a ship from the flag it flies,
while being faraway ashore, with the vessel in the middle of a gale and
dense fog.

One can maybe see some colors and shapes of the flag, but not in their entirety. It's ultimately a long game of analysis and exclusion of
implausible scenarios." HD1 is extremely bright in ultraviolet light. To explain this, "some energetic processes are occurring there or, better
yet, did occur some billions of years ago," Pacucci says.

At first, the researchers assumed HD1 was a standard starburst galaxy,
a galaxy that is creating stars at a high rate. But after calculating
how many stars HD1 was producing, they obtained "an incredible rate
-- HD1 would be forming more than 100 stars every single year. This
is at least 10 times higher than what we expect for these galaxies."
That's when the team began suspecting that HD1 might not be forming
normal, everyday stars.



==========================================================================
"The very first population of stars that formed in the universe were more massive, more luminous and hotter than modern stars," Pacucci says. "If
we assume the stars produced in HD1 are these first, or Population III,
stars, then its properties could be explained more easily. In fact,
Population III stars are capable of producing more UV light than normal
stars, which could clarify the extreme ultraviolet luminosity of HD1."
A supermassive black hole, however, could also explain the extreme
luminosity of HD1. As it gobbles down enormous amounts of gas, high
energy photons may be emitted by the region around the black hole.

If that's the case, it would be by far the earliest supermassive black
hole known to humankind, observed much closer in time to the Big Bang
compared to the current record-holder.

"HD1 would represent a giant baby in the delivery room of the early
universe," says Avi Loeb an astronomer at the Center for Astrophysics and co-author on the MNRAS study. "It breaks the highest quasar redshift on
record by almost a factor of two, a remarkable feat." HD1 was discovered
after more than 1,200 hours of observing time with the Subaru Telescope,
VISTA Telescope, UK Infrared Telescope and Spitzer Space Telescope.



==========================================================================
"It was very hard work to find HD1 out of more than 700,000 objects," says Yuichi Harikane, an astronomer at the University of Tokyo who discovered
the galaxy. "HD1's red color matched the expected characteristics of
a galaxy 13.5 billion light-years away surprisingly well, giving me
a little bit of goosebumps when I found it." The team then conducted
follow-up observations using the Atacama Large Millimeter/submillimeter
Array (ALMA) to confirm the distance, which is 100 million light years
further than GN-z11, the current record-holder for the furthest galaxy.

Using the James Webb Space Telescope, the research team will soon
once again observe HD1 to verify its distance from Earth. If current calculations prove correct, HD1 will be the most distant -- and oldest -- galaxy ever recorded.

The same observations will allow the team to dig deeper into HD1's
identity and confirm if one of their theories is correct.

"Forming a few hundred million years after the Big Bang, a black hole
in HD1 must have grown out of a massive seed at an unprecedented rate,"
Loeb says.

"Once again, nature appears to be more imaginative than we are."

========================================================================== Story Source: Materials provided by Harvard-Smithsonian_Center_for_Astrophysics. Note: Content may be edited
for style and length.


========================================================================== Related Multimedia:
* HD1_and_Timeline_of_earliest_galaxy_candidates ========================================================================== Journal References:
1. Yuichi Harikane, Akio K. Inoue, Ken Mawatari, Takuya Hashimoto,
Satoshi
Yamanaka, Yoshinobu Fudamoto, Hiroshi Matsuo, Yoichi Tamura, Pratika
Dayal, L. Y. Aaron Yung, Anne Hutter, Fabio Pacucci, Yuma Sugahara,
Anton M. Koekemoer. A Search for H-Dropout Lyman Break Galaxies
at z~12-16. The Astrophysical Journal (in press), 2022 [abstract]
2. Fabio Pacucci, Pratika Dayal, Yuichi Harikane, Akio K. Inoue,
Abraham
Loeb. Are the Newly-Discovered z~13 Drop-out Sources Starburst
Galaxies or Quasars? Monthly Notices of the Royal Astronomical
Society Letters, 2022 [abstract] ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220407101043.htm

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