by Using warped spacetime as a magnifying glass, astronomers have picked up the most distant signal of its kind from a distant galaxy, and it may blow up a window into how our universe was formed.
The record-breaking radio frequency signal, captured by the Giant Metrewave Radio Telescope (GMRT) in India, came from the galaxy SDSSJ0826+5630, located 8.8 billion light-years from Earth, meaning the signal was emitted when the universe was about a third of its current age.
The signal is an emission line from the universe’s most primordial element: neutral hydrogen. In the wake of The big bang, this element existed throughout the cosmos as a turbulent nebula from which the first stars and galaxies eventually formed. Astronomers have long searched for distant signals from neutral hydrogen in hopes of pinpointing the moment the first stars began to shine, but these signals have proven difficult to spot given the extraordinary distances involved.
Now, a new study, published December 23 in the journal Monthly Notices of the Royal Astronomical Society, (opens in a new tab) shows that an effect called gravitational lensing can help astronomers detect evidence of neutral hydrogen.
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“A galaxy emits different types of radio signals,” study lead author Arnab Chakraborty (opens in a new tab)a cosmologist at McGill University in Canada, said in a statement (opens in a new tab). “Until now, it has only been possible to capture this particular signal from a nearby galaxy, limiting our knowledge to those galaxies closer to Earth.”
The ‘Dark Ages’ of the Universe
Forged roughly 400,000 years after the beginning of the universe, when protons and electrons were first bound to neutrons, neutral hydrogen populated the dim early cosmos through its so-called dark ages, before the first stars and galaxies formed.
When stars form, they blast out intense ultraviolet light that strips the electrons from much of the hydrogen atoms in the space around them, thereby ionizing the atoms so that they are no longer neutral. Eventually, young stars lose their ultraviolet intensity, and some of the ionized atoms recombine into neutral hydrogen. Discovering and studying neutral hydrogen can provide insight into the lives of the earliest stars, as well as the era before stars existed.
Neutral hydrogen emits light at a characteristic wavelength of 21 centimeters. But using neutral-hydrogen signals to study the early universe is a tough task, as the long-wavelength, low-intensity signals are often drowned out over vast cosmic distances. Until now, the most distant 21 cm hydrogen signal detected was 4.4 billion light years away.
Gravitational lenses look into the past
To find a signal at twice the previous distance, the researchers turned to an effect called gravitational lensing.
In his theory of general relativelyAlbert Einstein explained it gravity is not produced by an invisible force, but rather is our experience of space-time curving and distorting in the presence of matter and energy. Gravitational lensing occurs when a massive object sits between our telescopes and the source. In this case, the space-distorting object was the giant star-forming galaxy SDSSJ0826+5630, which used its powerful twisting effect to act as a lens that steered a faint and distant neutral hydrogen signal into the focus of the GMRT.
“In this specific case, the signal is bent by the presence of another massive body, another galaxy, between the target and the observer,” study co-author Nirupam Roy, an associate professor of physics at the Indian Institute of Science, said in the statement. “This effectively results in a magnification of the signal by a factor of 30 so that the telescope can pick it up.”
Now that scientists have found a way to probe previously unreachable hydrogen clouds, they want to use it to improve their mapping of the universe through its various cosmological ages and hopefully pinpoint the moment the first stars began to shine.
