Reporting by David Xinpeng
A news explosion network of "Indian researchers received radio signals 9 billion light-years away for the first time" ranked first on the Zhihu hot list.
At press time, the topic has exceeded one million views and more than 100 answers.
Whether it is last year's JWST telescope or the recent hit "Three-Body Problem", the interest of people around the world in extraterrestrial civilization has always been increasing.
This time, did humanity get its wish?
Radio signal from 9 billion light-years
Researchers at McGill University and the Indian Institute of Science say they have captured radio signals from the most distant galaxy to date.
This is the first time humans have detected this type of radio signal at such a distance. McGill University said the radio waves could allow astronomers to "go back in time" and learn about the early universe and begin studying some of the earliest stars and galaxies.
The study was written by Arnab Chakraborty, a postdoctoral researcher at McGill University, and Nirupam Roy, an associate professor at the Indian Institute of Science. The study was published in the Monthly Proceedings of the Royal Astronomical Society (MNRAS), the top journal of astronomy.
Link to the paper: https://academic.oup.com/mnras/article/519/3/4074/6958817?login=false
The significance of this study is that for the first time, gravitational lensing has been used to detect H I 21 cm spectral lines in star-forming galaxies redshifted z = 1.3 (nearly 9 billion years ago). Until then, the most distant 21cm spectral line signal the researchers had detected was redshift z=0.4 (nearly 5 billion light-years).
The so-called 21 cm line, full name is the neutral hydrogen 21 cm line. It is also known as a "hydrogen line" and is a spectral line of electromagnetic radiation with a frequency of 1420.
The hydrogen atom has two ultra-fine structure sub-energy levels in its ground state. The collision of neutral hydrogen atoms in the ground state of interstellar matter causes a transition between these two sub-energy levels , forming radiation with 21 cm spectral lines.
The 21 cm line is the first line observed in radio astronomy and one of the most important. It is an important means of studying the distribution of interstellar neutral hydrogen atoms, the structure of the Milky Way and extragalactic galaxies.
The researchers say the telescope is able to pick up distant signals because it is bent by another galaxy located between the signal and the telescope. Nirupam Roy said that under gravitational lensing, the radio signal is amplified 30 times, allowing the telescope to successfully receive it.
The gravitational lensing effect is a phenomenon predicted by Einstein's general theory of relativity. Because space-time is distorted near massive objects, light bends as it passes near massive objects.
If there is a massive object in the observer's straight line to the light source, the observer will see one or more images formed due to the bending of the light, a phenomenon called gravitational lensing.
Simulating gravitational lensing
Not aliens, but ancient elements
The signal was detected by a giant meta-wave radio telescope in Pune, India. The telescope consists of 30 dishes pointing skyward, each nearly 150 feet in diameter.
This is the most distant signal ever recorded by tools on Earth, coming from a galaxy called SDSSJ0826+5630, located nearly 9 billion light-years away.
But it's not the E.T. aliens calling home. For scientists, it opens a window into the past and allows us to see what the universe looked like at its age (i.e. 13.7 billion years: estimated time after the Big Bang).
Researchers say the 8.8 billion-year-old radio wave did not come from an ancient alien race, but from one of the universe's most primitive elements: neutral hydrogen, which formed from the debris of the Big Bang about 400,000 years after the universe was born.
In the early days of the universe's formation, clouds of neutral hydrogen atoms scattered throughout the universe, what astronomers call the "Dark Ages" — the era before the first bright stars and galaxies emerged from celestial dust. Neutral hydrogen is the "fuel" for the emergence of these stars and galaxies.
"The neutral hydrogen reservoir provides the basic fuel for star formation in galaxies," reads a study of the telescope's findings published in the Monthly Notices of the Royal Astronomical Society. "To understand the evolution of galaxies in the universe, we need to understand the evolution of this neutral gas in the universe."
For decades, scientists have searched for traces of neutral hydrogen, hoping to determine when and how the first stars and galaxies appeared. But for years, search efforts have been limited because it is difficult for these electromagnetic signals to travel longer spaces and time to reach Earth.
According to LiveScience, the wavelength of electromagnetic radiation emitted by neutral hydrogen atoms is 21 centimeters, which belongs to the category of radio waves. Its longer wavelengths and lower frequencies are more likely to be submerged in the static of the universe.
The discovery set a record for the farthest distance humans have received a space signal, having previously detected the farthest signal of its kind from 4.4 billion light-years away.
Einstein was right again
To catch signals from twice the distance, the researchers drew on Einstein's theory of relativity, which suggests that the gravitational pull of matter and energy can distort space and time.
According to relativity, there is an effect called "gravitational lensing", in which a large mass, such as the signal source galaxy SDSSJ0826+5630, may distort the path of a distant radio signal to a scale that can be detected by detectors on our planet.
Nirupam Roy, associate professor of physics at the Indian Institute of Science and co-author of the paper, said in a statement:
"Gravitational lensing amplifies signals from distant objects and helps us peer into the early universe. In this case, the signal is bent due to the presence of another massive body between the target and the observer, another galaxy. This caused the signal to be amplified 30 times so that telescopes on Earth could pick it up."
The signal allows scientists to measure the gas composition of a distant galaxy, which is estimated to be twice the mass of any star visible from Earth.
And that's just the beginning, researchers trying to further untangle the clues of cosmic history hidden in the depths of space that we once had no control over.
"A galaxy emits many different radio signals."
Arnab Chakraborty, lead author of the study, said that so far, we have only been able to capture this particular signal from nearby galaxies, and our knowledge and vision are limited to those galaxy closer to Earth. But this time, with the help of gravitational lensing, we can capture a faint signal from a record-breaking distance. This will help us understand the composition of galaxies farther from Earth.
Advance! Advance!
This is not the first time scientists have received a mysterious signal from outer space.
Last July, astronomers at the Massachusetts Institute of Technology and other universities in the United States and Canada detected a persistent signal from a distant galaxy with astrophysical origins, and in 2020, a mysterious signal from the near constellation Centaurus made waves.
But do these signals mean that we are not alone? For now, at least, the answer is no – despite the signals already being sent into space.
According to the journal Nature, researchers said in 2021 that the Proxima Centauri signal may come from "artificial radio interference" and that the source of the "fast radio burst" signal may be radio pulsars or magnetars, both of which are types of neutron stars.
Daniele Michilli, a postdoctoral fellow at MIT's Kavley Institute for Astrophysics and Space, said there aren't many stars in the universe that emit signals strictly on a regular basis.
"In our own galaxy, the cases we know of are radio pulsars and magnetars. We think this new signal could be a magnet or pulsar on an asteroid."
The researchers received radio signals from 9 billion light-years away, as if glimpsing a flicker in the early universe.
And capturing this flicker may require the wisdom of all mankind.
Resources:
https://www.cbsnews.com/news/radio-signal-9-billion-light-years-away-captured-telescope-india-giant-metrewave-radio-telescope/
https://www.foxnews.com/science/radio-signal-9-billion-light-years-away-what-it-means-where-it-came-from
https://www.fastcompany.com/90838348/space-hydrogen-radio-signal-light-years-away
https://www.mcgill.ca/newsroom/channels/news/astronomers-capture-radio-signal-distant-galaxy-344925