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Astrophysicists count all the astronomical stars in the universe



The universe shines with light of several billion trillion stars. The astrophysic team recently used the satellite to compress all the light of those stars, measured in particles called photons. Let them be the numbers: Their estimate, through the history of the universe, the stars emitted four times the photon of 10 to 84.-the power in the visible universe (that's 4 followed by 84 zeros).

But their work was more than counting the sun's rays. Technology has enabled astrophysics to construct the star-forming history: The birth of the star reached about 3 billion years after a major burst, as members of the Fermi-LAT international co-operation reported on Thursday in Science. This shock has dramatically slowed down in more than 10 billion years.

Marco Ajello, astrophysicist at Clemson University in South Carolina and a large team of scientists working with the Fermi Gamma-ray Space Telescope, measured what is called extragalactic background light. "It's basically the whole show of all the stars in the universe," Ajello said.

The extragalactic backlight "is very precious for cosmologists," says Elisa Prandini, astrophysicist at the University of Padua, Italy, who was not involved in this research. "It encodes the history of the creation of the stars from the end of the" cosmic dark age, "hundreds of millions of years after the great burst, to this day."

For years, astronomers wanted to extract information from distant light beams. But extragalactic background light is very difficult to observe directly, as it is suppressing nearby emissions from the Sun's system and other stars of the Milky Way galaxy. So Ajello and his team measured the star's proxy light, with the aid of gamma ray.

The stars are formed in the cradle of gas and dust. This cradle absorbs some light. But the rest of the light particles, the photons in visible and ultraviolet wavelengths, are overwhelmed in the glow of the universe. Not all of their travels are a peaceful end. For example, if the star's light approaches gamma radiation, the result is the destruction that creates new particles.

Gamma rays are also made of photons, although they have enormous amounts of energy, up to trillion times more than visible light. Blazers, or super-massive black holes in the center of the galaxy, emit gamma rays when the substance near these black holes slashes and drops.

These collisions work for the benefit of astronomers. "If you have gamma-air, this will only interact with photons in the starlight," Ajello said. The starlight in essence "absorbs" gamma rays, similar to the way the gases in the Earth's atmosphere absorb light from the sun. The gamma-ray detector on the Fermi Observatory can observe how these beams are losing energy when they destroy starlight. Measuring this absorption, this energy loss is a sign that the rays favor stellar photons. And soon: the way of calculating the star of light.

The team used 739 blazers to explore starlight through history. The farthest blazar was created 200 million years ago. The closest blazer gave the scientists a recent look like 11.6 billion years after the big noise. (The universe is about 13.8 billion years old.) The stars really began to flourish when the universe was only two billion years old. The creation of a star reached a peak of one billion years later, and then began to fall slowly as it was gone.

That peak of star formation corresponds to independent measurements by other telescopes, Prandini said. That's good news, she said, because that means "we actually look at almost all the galaxies that inhabit the recent universe."

Moreover, this "excellent set of data" of extraordinary backlight still contains more information to be investigated, Prandini said. It could be used to measure other cosmological values, such as the Hubble constant (which describes the spread of the universe) and all matter, including dark matter, in the universe.

Though this technique has given insight into the early ages of the universe, the first billion years are still poorly known. Because of this, Ajello said, astrophysicists are eagerly anticipating a long delay in the launch of the telescope James Webb, which will investigate further stars – and long ago in time.

© Washington Post 2018

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