With the help of a radio telescope in India, a team of astronomers detected for the first time the emission of hydrogen atoms in a galaxy that was produced 8 million years ago near the peak of the “assembly” of these objects. This discovery helps to understand why the formation of so many stars was later reduced that they used increasingly scarce hydrogen as fuel.
The astrophysics community has learned from the research of optical telescopes and infrared telescopes that the formation of stars in the universe has reached its peak in the past two decades. 8 and 10 billion years. After that, the formation of stars and galaxies was much slower. This is why almost half of the mass of stars that can be observed today come from the period of maximum activity, which is the so-called “Era of Galaxy Assembly.”
In the last 8 billion years, the reason for this decrease in star formation remains unclear.One of the reasons is Little information About him Neutral atom hydrogen (H or HI), the main fuel for the formation of stars in the galaxy at that time, Redshift Very high-that is, as the universe expands, the distance between them is getting farther and farther. Atomic hydrogen is in its molecular state (H2 pcs), finally, in star.
The best way to track the existence of this situation Neutral atom hydrogen Is by detecting its footprint in the electromagnetic spectrum, called HI or 21 cm line Through its wavelength. This type of tracking has never been performed when the redshift of stars formed long after the galactic buildup is greater than 0.4.
But now, Indian researchers have published an article in the latest issue of “Science” natural 21cm line of radiation was detected for the first time in the Milky Way Redshift 1, Very close to the peak of star formation. These findings provide new clues about what happened to this fuel 8 billion years ago and increase the astrophysical community’s understanding of the evolution of galaxies.
Nissim Kanekar ÿ Aditya Chowdhury, The co-author of this work and from National Radio Astrophysics Center In Pune, India, they explained to SINC that after this assembly period, there are not enough hydrogen atoms in the galaxy to sustain all star formation activities for more than one or two billion years. “Once I know sold out They described in detail “this fuel causes the rapid decline of star formation”.
Search for atomic hydrogen in 7,653 galaxies
The biggest problem with detecting the 21 cm line of radiation is that it is very weak, so it is difficult to find the atomic hydrogen in more distant galaxies.To solve this problem, the team used Giant wave radio telescope (GMRT, the most sensitive radio interferometer used to observe these radiations) and stack analysis technology, which combines radiation from many galaxies (7,653 in this case) to increase the signal strength by 21 cm.
This Stack analysis Allows to determine the average properties of the population (e.g. galaxies) and is the only way to detect the amount and distribution of atomic hydrogen before the next generation of radio telescopes (e.g., telescopes) Square kilometer array. However, this technology does not provide details of the following: Single object , But get average estimates from the data set and are limited to galaxies that can be detected in the optical band.
“This technology allows us to detect a signal of 21 cm in a reasonable time. If we want to know the radiation from a single galaxy at this distance, we will have to use the world’s best telescope to observe for more than 10,000 hours. It’s almost impossible,” Kanekar pointed out.
In the evaluation of this study, naturalChris L. Carilli, a researcher at the National Radio Astronomy Observatory in the United States, pointed out: “These measurements of the weak radio radiation emitted by distant galaxies reveal the nature of the gas that promoted the galaxy’s largest formation age, and pointed out the reasons Since then, the rate of star formation has declined. The author has filled the gap in our knowledge of the formation of the Milky Way.”
Chowdhury, A. Et al. “Hi 21 cm emission from a collection of galaxies has an average redshift of 1”. natural.