A small group of astronomy researchers have just found traces of hydrogen “at an impossible distance” 9 billion light-years away. According to the laws of current physics, such an observation is normally impossible.
This natural constraint had restricted research on hydrogen in space to galaxies close to the Earth such as Andromeda or the Magellanic cloud. A few rare studies had tried to go further, setting an observation record around 5 billion light-years. Beyond that, the radio wave disappears before reaching the Earth.
Arnab Chakraborty, co-author of the study and professor of cosmology for McGill University (Montreal, Canada) was however not discouraged by this natural barrier. He used the laws of gravity to his advantage to find hydrogen more than 9 billion light-years from Earth.
Long distance observation
The hydrogen observation carried out by the Chakraborty teams © Chakraborty & Roy, GMRT/NCRA-TIFR)
At such a distance from its target, India’s Meterware radio telescope picks up radio waves that are 9 billion years old. They have traveled for millennia in the vacuum of space before reaching us. By forming this shot, they allow us to go back in time.
Scientists then discover the Universe as it was 9 billion years ago, during its adolescence. Focused on the “21cm line” radio wave, the signature of hydrogen, the image (above) makes it possible to find a concentration of this gas.
Behind this tiny red dot, hundreds of galaxies hide, containing billions of stars and as many planets. By knowing the distribution of hydrogen at such a distant period, scientists can pinpoint the expansion patterns of the Universe and go back in time more accurately.
A gravitational magic trick
The principle of gravitational lens discovered by Einstein makes it possible to study normally invisible galaxies © Swadha Pardesi
This does not, however, explain how such an observation was made possible. In reality, Chakraborty did not invent anything, he even used a law known for more than a century. Theoretically described by Albert Einstein almost 100 years ago, the principle of gravitational lenses is a real cosmic magic trick. It is the result of a “deviation” of light by gravity.
In other words, if a distant galaxy encounters a massive object in its path, then the light will “circle” it due to gravity (see above). This principle allowed the Chakraborty teams to study a region of the sky 9 billion years old. The radio wave bypassed another galaxy before arriving on Earth.
