Credit: Thomas Müller (HdA/MPIA) and
Thavisha Dharmawardena (NYU)
An
international team of scientists led by a Rutgers University–New Brunswick
astrophysicist has discovered a potentially star-forming cloud that is one of
the largest single structures in the sky and among the closest to the sun and
Earth ever to be detected.
The vast ball of hydrogen, long invisible to scientists, was revealed by
looking for its main constituent: molecular hydrogen. The finding marks the first time a molecular cloud has been detected with light emitted in the
far-ultraviolet realm of the electromagnetic spectrum and opens the way to
further explorations using the approach.
The scientists have named the molecular
hydrogen cloud "Eos," after the Greek goddess of mythology, who is
the personification of dawn. Their discovery is outlined in a study published in Nature
Astronomy.
"This opens up new possibilities for studying the molecular universe," said Blakesley Burkhart, an associate professor in the Department of Physics and Astronomy in the Rutgers School of Arts and Sciences who led the team and is an author on the study. Burkhart is also a research scientist at the Center for Computational Astrophysics at the Flatiron Institute in New York.
Scientists have discovered a potentially
star-forming cloud and called it "Eos." It is one of the largest
single structures in the sky and among the closest to the sun and Earth ever to
be detected. Credit: Thomas Müller (HdA/MPIA) and Thavisha Dharmawardena (NYU)
Molecular clouds are composed of
gas and dust—with the most common molecule being hydrogen, the fundamental
building block of stars and planets and essential for life. They also contain
other molecules such as carbon monoxide. Molecular clouds are often detected
using conventional methods such as radio and infrared observations that easily
pick up the chemical signature for carbon monoxide.
For this work, the scientists
employed a different approach.
"This is the first-ever
molecular cloud discovered by looking for far ultraviolet emission of molecular
hydrogen directly," Burkhart said. "The data showed glowing hydrogen
molecules detected via fluorescence in the far ultraviolet. This cloud is
literally glowing in the dark."
Eos poses no danger to Earth and
the solar system. Because of its proximity, the gas cloud presents a unique
opportunity to study the properties of a structure within the interstellar medium, scientists said.
The interstellar medium, made of
gas and dust that fills the space between stars within a galaxy, serves as raw
material for new star formation.
"When we look through our
telescopes, we catch whole solar systems in the act of forming, but we don't
know in detail how that happens," Burkhart said. "Our discovery of
Eos is exciting because we can now directly measure how molecular clouds are
forming and dissociating, and how a galaxy begins to transform interstellar gas
and dust into stars and planets."
The crescent-shaped gas cloud is
located about 300 light years away from Earth. It sits on the edge of the
Local Bubble, a large gas-filled cavity in space that encompasses the solar
system. Scientists estimate that Eos is vast in projection on the sky,
measuring about 40 moons across the sky, with a mass about 3,400 times that of
the sun. The team used models to show it is expected to evaporate in 6 million
years.
"The
use of the far ultraviolet fluorescence emission technique could rewrite our
understanding of the interstellar medium, uncovering hidden clouds across the
galaxy and even out to the furthest detectable limits of cosmic dawn,"
said Thavisha Dharmawardena, a NASA Hubble Fellow at New York University and a
shared first author of the study.
Eos was revealed to the team in data
collected by a far-ultraviolet spectrograph called FIMS-SPEAR (an acronym for
fluorescent imaging spectrograph) that operated as an instrument on the Korean
satellite STSAT-1. A far-ultraviolet spectrograph breaks down far-ultraviolet
light emitted by a material into its component wavelengths, just as a prism
does with visible light, creating a spectrum that scientists can analyze.
The data had just been released publicly
in 2023 when Burkhart came across it.
"It was kind of like just waiting
to be explored," she said.
The findings highlight the importance of
innovative observational techniques in advancing the understanding of the
cosmos, Burkhart said. She noted that Eos is dominated by molecular hydrogen
gas but is mostly "CO-dark," meaning it doesn't contain much of the
material and doesn't emit the characteristic signature detected by conventional
approaches. That explains how Eos eluded being identified for so long,
researchers said.
"The story of the cosmos is a story
of the rearrangement of atoms over billions of years," Burkhart said.
"The hydrogen that is currently in the Eos cloud existed at the time of
the Big Bang and eventually fell onto our galaxy and coalesced near the sun.
So, it's been a long journey of 13.6 billion years for these hydrogen
atoms."
The discovery presented itself as
something of a surprise.
"When I was in graduate school, we
were told that you can't easily directly observe molecular hydrogen," said
Dharmawardena of NYU. "It's kind of wild that we can see this cloud in
data that we didn't think we would see."
Eos also is named after a proposed NASA
space mission that Burkhart and other members of the team are supporting. The
mission aims to broaden the approach of detecting molecular hydrogen to greater
swaths of the galaxy, investigating the origins of stars by studying the
evolution of molecular clouds.
The team is scouring data for molecular
hydrogen clouds near and far. A study published as a preprint on arXiv by Burkhart and others using the James Webb
Space Telescope (JWST) reports tentatively finding the most distant molecular
gas yet.
"Using JWST, we may have found the very furthest hydrogen molecules from the sun," Burkhart said. "So, we have found both some of the closest and farthest using far-ultraviolet emission."
Source: A vast molecular cloud, long invisible, is discovered near our solar system
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