Gravitational lensing reveals dark matter 12 billion years old – New Scientist

Japanese scientists have mapped the distribution of dark matter in galaxies for about 12 billion years. To do this, scientists used gravitational lensing and cosmic microwave background radiation.

We have “lost” about 85 percent of the universe. With our measuring instruments, we can only observe 15 percent of all material. The rest is invisible because it emits no measurable radiation. But we know it must be there because its gravity clearly affects the motion of stars and galaxies. We call these mysterious untraceable things dark matter.

There appears to be some sort of dark matter halo around most galaxies. Its gravity holds the stars in the galaxy together. Without the corona, the outer stars would be ejected into space due to the speed at which the galaxy rotates.

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Japanese scientists have been studying dark matter halos since the universe was still young. This study has two main reasons. “First of all, we want to know how (the first) galaxies form in regions with a high density of dark matter,” the cosmologist said by email. Hironao Miyatake from Nagoya University in Japan. “We also want to know how the structure of the universe has changed from the Big Bang to today.”

dark halos

The only way astronomers can study dark matter haloes is by measuring the effect of their gravity on the environment. This is exactly what Japanese astronomers have done now. As for the dark matter surrounding (and inside) galaxies that formed 12 billion years ago, less than 2 billion years after the Big Bang. To see so far into the past, they use the effect of the gravitational curvature of spacetime, background radiation left over from the Big Bang and a powerful telescope.

You can look back in time. This is because light travels at about 300,000 kilometers per second. It therefore takes one second to cover 300,000 km. The further away the light source is, the longer it takes for its light to reach us. For example, it takes eight minutes for sunlight to reach us. As a result, we “see” the Sun as it appeared eight minutes ago.

If you look very far into the universe, you can find light from galaxies that traveled 12 billion years ago. So you can see galaxies as they looked 12 billion years ago.

Gravity lenses

Okay, but how do you measure dark matter in these distant galaxies? To measure the dark matter aura in a galaxy, light from galaxy after galaxy is often used, which is of interest to researchers. The gravity of the galaxy in front of us, determined by the combination of visible and dark matter, distorts the space-time around this galaxy. This effect, predicted by Einstein in his general theory of relativity, is comparable to a heavy bowling ball on a trampoline. The trampoline’s canvas is deformed around the bowling ball.

When light from a distant galaxy travels through curved space-time to a foreground galaxy, it is deflected. Then the system in the foreground works as a “gravitational lens”. The light is bent in a similar way as a normal lens.

The more dark matter in a galaxy, the more the light bends. This allows astronomers to infer how much dark matter the next galaxy contains.

For the above technique you need a galaxy that is very far away and therefore older than the galaxy in front of you. These distant and ancient galaxies are rare and faint, making measurements in distant and ancient galaxies difficult. That makes it difficult to look back more than eight to ten billion years.

Schematic representation of a gravitational lens. Light from a light source bends around a heavy object. The white arrows show the path the light takes from its source around a heavy object. The orange arrows show where the backlight source appears in front of the viewer. Source: Wikimedia Commons, NASA/European Space Agency.

cosmic microwave background radiation

Japanese scientists found something in it. They are not using a distant galaxy as their light source, but the cosmic microwave background, which is everywhere in the universe. This is the first light. It erupted more than 13.6 billion years ago from the primordial soup that formed the universe immediately after the Big Bang.

with the Japanese Subaru telescope The researchers selected lens galaxies so far away that we can see them as they looked 12 billion years ago.

Miyatake says that the effect of the inversion of the gravitational field of a single distant galaxy against the background of cosmic cosmic waves is very small. “Therefore, we set up an average of about 1.5 million galaxies to measure the lensing signal.” They then compared the signal with a theoretical model that predicts what the distribution of dark matter around these galaxies should look like. “Our measurements turned out to agree very well,” says Miyatake.

Japanese researchers have shown with their results that it is possible to measure the dark matter halos in galaxies in the early universe in this way.

“This is an exciting new type of measurement,” says the cosmologist. Hendrik Hildebrandt from the Ruhr University in Bochum and was not involved in the study. This confirms it proof of concept he. These first results have not yet produced any new scientific discoveries. “It shows what is possible with future measurements.”

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