Cosmic dawn, when stars formed for the first time, occurred 250 million to 350
million years after the beginning of the universe, according to a new study
led by researchers at University College London (UCL) and the University of
Cambridge.
The study, published in the Monthly Notices of the Royal Astronomical
Society, suggests that the NASA James Webb Space Telescope (JWST), scheduled
to launch in November, will be sensitive enough to observe the birth of
galaxies directly.
The UK-led research team examined six of the most distant galaxies currently
known, whose light has taken most of the universe's lifetime to reach us.
They found that the distance of these galaxies away from Earth corresponded
to a "look back" time of more than 13 billion years ago, when the universe
was only 550 million years old.
Analyzing images from the Hubble and Spitzer Space Telescopes, the
researchers calculated the age of these galaxies as ranging from 200 to 300
million years, allowing an estimate of when their stars first formed.
Lead author Dr. Nicolas Laporte (University of Cambridge), who started the
project while at UCL, said: "Theorists speculate that the universe was a
dark place for the first few hundred million years, before the first stars
and galaxies formed.
"Witnessing the moment when the universe was first bathed in starlight is a
major quest in astronomy.
"Our observations indicate that cosmic dawn occurred between 250 and 350
million years after the beginning of the universe, and, at the time of their
formation, galaxies such as the ones we studied would have been sufficiently
luminous to be seen with the James Webb Space Telescope."
The researchers analyzed starlight from the galaxies as recorded by the
Hubble and Spitzer Space Telescopes, examining a marker in their energy
distribution indicative of the presence of atomic hydrogen in their stellar
atmospheres. This provides an estimate of the age of the stars they contain.
This hydrogen signature increases in strength as the stellar population ages
but diminishes when the galaxy is older than a billion years. The
age-dependence arises because the more massive stars that contribute to this
signal burn their nuclear fuel more rapidly and therefore die first.
Co-author Dr. Romain Meyer (UCL Physics & Astronomy and the Max Planck
Institute for Astronomy in Heidelberg, Germany) said: "This age indicator is
used to date stars in our own neighborhood in the Milky Way but it can also
be used to date extremely remote galaxies, seen at a very early period of
the universe.
"Using this indicator we can infer that, even at these early times, our
galaxies are between 200 and 300 million years old."
In analyzing the data from Hubble and Spitzer, the researchers needed to
estimate the "redshift" of each galaxy which indicates their cosmological
distance and hence the look-back time at which they are being observed. To
achieve this, they undertook spectroscopic measurements using the full
armory of powerful ground-based telescopes—the Chilean Atacama Large
Millimetre Array (ALMA), the European Very Large Telescope, the twin Keck
telescopes in Hawaii, and Gemini-South telescope.
These measurements enabled the team to confirm that looking at these
galaxies corresponded to looking back to a time when the universe was 550
million years old.
Co-author Professor Richard Ellis (UCL Physics & Astronomy), who has
tracked ever more distant galaxies over his career, said: "Over the last
decade, astronomers have pushed back the frontiers of what we can observe to
a time when the universe was only 4% of its present age. However, due to the
limited transparency of Earth's atmosphere and the capabilities of the
Hubble and Spitzer Space Telescopes, we have reached our limit.
"We now eagerly await the launch of the James Webb Space Telescope, which we
believe has the capability to directly witness cosmic dawn.
"The quest to see this important moment in the universe's history has been a
holy grail in astronomy for decades. Since we are made of material processed
in stars, this is in some sense the search for our own origins."
The new study involved astronomers at the University of California-Santa
Cruz, the University of California, and the University of Texas.
The NASA-led James Webb Space Telescope, the successor to the Hubble
observatory, is scheduled to be launched into space in November. It will be
the premier observatory over the next decade, serving thousands of
astronomers worldwide. It consists of an infrared observatory, an immense
mirror 6.5 meters wide, and a diamond-shaped sunshield. UCL scientists at
the Mullard Space Science Laboratory have built and tested key hardware
components for the NIRSpec (Near-Infrared Spectrograph), one of the
telescope's four instruments.
Reference:
N Laporte et al, Probing cosmic dawn: Ages and star formation histories of
candidate z ≥ 9 galaxies, Monthly Notices of the Royal Astronomical Society
(2021). DOI:
10.1093/mnras/stab1239
Tags:
Space & Astrophysics