A red glowing object in the early universe has been identified as the farthest galaxy yet discovered.
Astronomers revealed that it was a galaxy that existed only 330 million years after the Big Bang. Its dim light, stretched by the expansion of the universe, had to travel 13.5 billion light-years to reach us, here on Earth.
The discoverers named the galaxy HD1, and it represents a bit of a mystery. And scientists aren’t quite sure what a galaxy is: whether it’s a star galaxy, which oscillates favorably with star formation, or a quasar, with an active supermassive black hole at its center.
If this is the latter, then the black hole’s growth to massive size soon after the universe came into existence poses a challenge to models of black hole formation and evolution.
“Answering questions about the nature of a very distant source can be difficult,” says astrophysicist Fabio Paccucci, of the Harvard-Smithsonian Center for Astrophysics.
Detecting things from the early universe is very difficult. Even quasars, the brightest objects in the entire universe, are so faint across vast swaths of space-time that our most powerful telescopes struggle to catch their light.
HD1 was discovered as part of a survey to discover galaxies in the early universe, the results of which are detailed in a paper accepted for publication in The Astrophysical, also available on arXiv.
Analysis of HD1 and a second galaxy called HD2, about a distance away, has been accepted in the Monthly Notices of the Royal Astronomical Society, and is also available on arXiv.
The survey used four powerful optical and infrared telescopes: the Subaru telescope, the Vesta telescope, the UK infrared telescope, and the Spitzer Space Telescope. In between, she spent more than 1,200 hours of observing time, gazing at the cosmic dawn to search for light in the early universe.
“It was very difficult to find HD1 out of more than 700,000 objects,” says astronomer Yuichi Harikan, from the University of Tokyo in Japan. “The red color of HD1 matches the expected properties of a galaxy surprisingly 13.5 billion light-years away, which gave me goosebumps when I found it.”
The red color is known as redshift, and it occurs when a light source moves away from us. This increases the wavelength of light coming from this source towards the red end of the electromagnetic spectrum, which is why it is called redshift.
Because the universe is expanding, other galaxies appear redshifted. The greater the distance in spacetime, the greater the redshift. This effect allows astronomers to calculate the distance the light has traveled to reach us.
But the light from the HD1 is baffling. It is very bright at ultraviolet wavelengths, indicating that a very energetic process was taking place within the galaxy. At first, the researchers thought it was the normal activity of a starburst – until they calculated how many stars would have to form to produce that much light.
The number was incredibly high, more than 100 stars a year. This is ten times higher than expected for a galaxy in the early universe. However, this tension can be resolved, if the stars that are born are not the same as the stars we see being born today.
“A black hole in HD1 formed a few hundred million years after the Big Bang, and it must have grown from a massive seed at an unprecedented rate,” says astrophysicist Avi Loeb of the Harvard and Smithsonian Center for Astrophysics.
The team hopes that future observations using the James Webb Space Telescope will reveal the nature of this mysterious dawn light.