Astronomers have seen the most distant galaxy

An international team of astronomers, including researchers from the Center for Astrophysics | Harvard and the Smithsonian discovered the most distant astronomical object ever observed: a galaxy.

Named HD1, the Master Galaxy is about 13.5 billion light-years away and is described in the Astrophysical Journal on Thursday. In an accompanying article published in the Monthly Notices of the Royal Astronomical Society Letters, scientists began to speculate on the exact nature of the galaxy.

The team proposes two ideas: HD1 could form stars at an astonishing rate and accommodate population III stars, the very first stars in the universe that have never been observed until now. Or HD1 could contain a supermassive black hole with a mass about 100 million times our sun.

“Answering questions about the nature of such a distant source can be a challenge,” said Fabio Pacucci, lead author of the MNRAS study, co-author of the paper on the discovery of ApJ and astronomer at the Center d’astrophysics. “It’s like guessing a ship’s nationality from the flag it’s flying while it’s far ashore, with the ship in the middle of a gale and dense fog. We may see some colors and shapes on the flag, but not in their entirety. It is ultimately a long game of analyzing and excluding unlikely scenarios. »

HD1 is extremely bright in ultraviolet light. To explain it: “certain energy processes take place there or, even better, took place there a few billion years ago,” says Pacucci.

Initially, the scientists assumed that HD1 was a standard eruption galaxy, that is, a galaxy that creates high-speed stars. But after calculating the number of stars produced by HD1, they got “an incredible speed – HD1 would form more than 100 stars each year. This is at least 10 times more than what we expect for these galaxies”.

That was when the team began to form suspicions that HD1 might not be forming normal everyday stars.

“The very first population of stars formed in the universe was more massive, brighter and warmer than modern stars,” says Pacucci. “Assuming the stars produced in HD1 are these early stars or population III stars, then its properties could be more easily explained. In fact, population III stars are capable of producing more UV light than normal stars, which could explain HD1’s extremes. ultraviolet brightness. »

However, a supermassive black hole could also explain the HD1’s extreme brightness. By engulfing huge amounts of gas, high-energy photons could be emitted from the area around the black hole.

If so, it would be by far the earliest supermassive black hole known to mankind, observed much closer to the Big Bang than the current record holder.

“HD1 would represent a giant baby in the natal space of the early universe,” said Avi Loeb, an astronomer at the Center for Astrophysics and co-author of the MNRAS study. “It beats the highest quasar redshift ever recorded by a factor of nearly two, a remarkable feat.”

HD1 was discovered after more than 1,200 hours of observation with the Subaru Telescope, the VISTA Telescope, the British Infrared Telescope and the Spitzer Space Telescope.

“It was a very difficult task to find HD1 among more than 700,000 objects,” said Yuichi Harikane, an astronomer at the University of Tokyo who discovered the galaxy. “The red color of HD1 matched surprisingly well the expected characteristics of a galaxy 13.5 billion light-years away, giving me a little goosebumps when I found it.”

The team then made follow-up observations using the Atacama Large Millimeter / Submillimeter Array (ALMA) to confirm the distance, which is 100 million light-years away from GN-z11, the holder of the current record for the most distant galaxy.

Using the James Webb Space Telescope, the research team will soon be observing HD1 again to check its distance from Earth. If current calculations prove correct, HD1 will be the most distant – and oldest – galaxy ever.

The same observations will allow the team to dig deeper into the identity of HD1 and confirm whether any of their theories are correct.

“Formed a few hundred million years after the Big Bang, the black HD1 hole must have grown from a massive seed at an unprecedented rate,” Loeb explains. “Again, nature seems to be more imaginative than us.”

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