"We discovered a galaxy which formed 15 billion times the mass of the sun in stars and then stopped forming stars before the universe was only 700 million years old."
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The record-breaking early galaxy RUBIES-UDS-QG-z7 and its
spectra as seen by the JWST. (Image credit: NASA/CSA/ESA, A. Weibel, P. A.
Oesch (University of Geneva), RUBIES team: A. de Graaff (MPIA Heidelberg), G.
Brammer (Niels Bohr Institute), DAWN JWST Archive) |
Using the James Webb Space Telescope (JWST), astronomers
have found the most distant (and thus the earliest) massive "dead"
galaxy to date. The discovery suggests that galaxies were "dying"
much earlier in the universe than previously believed.
"Death" for a galaxy refers to the slowing down,
or even halting, of intense star formation, which stops a galaxy from growing.
Such dead galaxies are more formally referred to as being
"quiescent," or "quenched." Early dead galaxies seen by the
JWST have been referred to as "red and dead" galaxies due to their
lack of massive hot young blue stars and their abundance of old small red
stars. They have also been dubbed "Little Red Dots" due to their
appearance in JWST images.
Light from this new record-breaking galaxy, designated
RUBIES-UDS-QG-z7, has been traveling to us for 13 billion years, meaning the
JWST saw it as it was just 700 million years after the Big Bang. That makes it
the first so-called massive quiescent galaxy (MQG) seen in the infancy of the
13.8 billion-year-old universe.
"We discovered a galaxy which formed 15 billion times
the mass of the sun in stars and then stopped forming stars before the universe
was only 700 million years old," team member Andrea Weibel of the
University of Geneva (UNIGE) Department of Astronomy told Space.com. "This
makes RUBIES-UDS-QG-z7 the most distant massive quiescent galaxy known to
date."
The discovery may challenge our models of how galaxies
evolve — and eventually stop growing — due to the cessation of star birth.
"The observation implies that some galaxies have
stopped forming stars when the universe was only 700 million years old,"
Weibel said. "So far, models and simulations contain very few such
objects, more than 100 times fewer than the existence of RUBIES-UDS-QG-z7
suggests. This means that the physical processes and mechanisms that regulate
star formation and its termination in galaxies in the early universe may have
to be revisited."
Live fast; die young.
Quiescent galaxies are common immediately around the Milky
Way. That's expected because the further away we look, the further back in time
we are traveling. Thus, local massive galaxies have had a lot of time to start
forming stars, grow to tremendous masses, and then exhaust the gas and dust
needed for stellar construction, thus becoming quenched. We should expect more
distant galaxies to still be enjoying their star-birthing youth.
As the JWST has probed further and further back in time,
however, it has discovered earlier and earlier MQGs. Several of these red and
dead galaxies were found as early as 1.2 billion years after the Big Bang.
Discovered as part of the "Red Unknowns: Bright Infrared Extragalactic
Survey," or RUBIES, program, RUBIES-UDS-QG-z7 pushes the detection of MQGs
back by another 500 million years.
"Massive galaxies observed early in the universe only
had a very limited amount of time to form their stars. This means they must
have formed rapidly and efficiently, which helps us to constrain and, in some
cases, even challenge theories and models of galaxy formation and growth,"
Weibel said. "RUBIES-UDS-QG-z7, however, is not only massive but has
already stopped forming stars 50 to 100 million years before we observe it,
while normal galaxies at these epochs are still building up their stellar mass
through star formation."
Weibel explained that the mass of RUBIES-UDS-QG-z7 and its
reconstructed formation history suggest relatively efficient star formation for
the galaxy. That does not directly challenge existing models of star formation.
"The galaxy is very compact and may be an example of an
object where a lot of gas and dust — the fuel of star formation — collapses and
assembles into a small volume, where stars can form rapidly and efficiently for
an extended period of time, or in multiple bursts," Weibel said.
"What makes RUBIES-UDS-QG-z7 stand out is that it stopped forming stars so
early on."
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Three spectra taken by the JWST/NIRSpec superimposed on an
image taken by the JWST/NIRCam, two instruments on board the James Webb Space
Telescope. The record galaxy is shown in the middle. (Image credit:
NASA/CSA/ESA, A. Weibel, P. A. Oesch (University of Geneva), RUBIES team: A. de
Graaff (MPIA Heidelberg), G. Brammer (Niels Bohr Institute), DAWN JWST Archive) |
This MQG may stand out from Little Red Dots seen by the JWST
in ways other than its rapid death.
"In the JWST images, RUBIES-UDS-QG-z7 resembled objects
named Little Red Dots, which have been discovered with the JWST," Weibel
said. "Many of these objects turned out to have strong emission lines
and/or showed signs of active galactic nuclei (AGN). Thus, at least a good
fraction of the light we observe from Little Red Dots may actually originate
from accreting supermassive black holes, rather than stars."
However, Weibel added that RUBIES-UDS-QG-z7 shows no signs
of an AGN, meaning its light comes entirely from stars, not from the violent
conditions around a feeding black hole.
"This then implies its rather high mass and its
quiescence, which both came as a big surprise," Weibel continued. "So
far, we have only found one such object in all the JWST data that we
investigated."
From this, the team calculated that galaxies like
RUBIES-UDS-QG-z7 should account for around one in 1 million galaxies.
"This is, however, quite uncertain, because we don't
know how lucky we got to find one in the small patch of the sky that we have
scanned so far," Weibel said. "With hopefully many more years of JWST
taking data, we will be able to search larger areas of the sky and get a better
idea of how common galaxies like RUBIES-UGD-QG-z7 actually are."
Performing higher resolution and deeper spectroscopy imaging
of this galaxy could reveal the abundances of various elements, which would
help better constrain the formation history of RUBIES-UDS-QG-z7.
"We will get more data on this galaxy in the upcoming
Cycle 4 of JWST observations. Specifically, higher resolution
spectroscopy," Weibel said.
The JWST may need a helping hand to study RUBIES-UDS-QG-z7
from Earth's largest radio telescope project, the Atacama Large
Millimeter/submillimeter Array (ALMA), which consists of 66 antennas located in
the Atacama Desert region of Northern Chile.
"Data from the ALMA telescope at longer wavelengths of
light can give us direct insight into the gas and dust content of the galaxy,
which is closely related to its past and future star formation history,"
Weibel said.
The team's research was published on April 1 in TheAstrophysical Journal.