Monday , June 21 2021

Quasi-gravitational lenses quasars could finally help to understand how fast the universe is expanding



How fast does the universe expand? This is a question astronomers are unable to answer accurately. They have a name for the speed of expansion of the universe: the Hubble constant or the Hubble Act. But the measurements continue to go with different values ​​and astronomers have been debating back and forth on this issue for decades.

The basic idea behind the Hubble Constant Measurement is to look at distant light sources, usually a kind of supernovae or variable stars, called "standard candles", and measure the red light shift. But no matter how astronomers do, they can not come out with agreed value but only with a set of values. A new study, including quasars and gravitational lenses, can help solve the problem.

The fact that the universe is expanding is not in question. We have known this for about 100 years. The light from distant galaxies is moved to red as they move away from us, and the measurement of red-shifting has led to different values ​​for universal expansion.

"Hubble constantly attaches the physical scale to the universe."


Simon Beerr, postdoctoral and lead author of the study.

The rate of expansion is measured in kilometers per second of mega-parse, recorded as (km / s) / Mpc. For example, something that expands at a speed of 10 (km / s) / Mpc means that two points in space of 1 mega-parse than each other (equivalent to 3.26 million light-years) rise from each other at a speed of 10 kilometers per second.

When first discovered in the 1920s, the expansion rate is considered to be 625 kps / Mpc. But since the 1950s, better research measured it as less than 100 kps / Mpc. Over the last few decades, numerous studies have measured the speed of expansion and have reached speeds of between 67 and 77 kps / Mpc.

But science will not accept a set of answers for something that should have one value. It would not be science if it did. So scientists are trying to test different ways to measure the Hubble constant to see if they can do it properly because the Hubble constant is more than just measuring the expansion of the universe.

"Hubble constantly attaches the physical scale of the universe," said Simon Beer, a PhD student and lead author of the study. Without the exact value of Hubble's constant, astronomers can not accurately determine the dimensions of the distant galaxies, the age of the universe or the history of space expansion. So doing it is a big deal.

A new study, published in the monthly announcements of the Royal Astronomical Society, is trying to use a new method of measuring the Hubble constant. The research is led by a team of astronomers in Los Angeles and relies on far quasars whose light undergoes gravitational lensing before reaching the Earth.

The impression of ULAS artist J1120 + 0641, a very remote quasar, driven by a black hole with a mass two billion times greater than that of the Sun. Regards: ESO / M. Kornmesser
The impression of ULAS artist J1120 + 0641, a very remote quasar, driven by a black hole with a mass two billion times greater than that of the Sun. Regards: ESO / M. Kornmesser

Quasars are ultra-bright objects. They are also called active galactic cores because they are believed to be caused by supermassive black holes in the center of galaxies. The electromagnetic radiation they emit is caused by the rotating disk of accumulation around the black hole. As the disk around the hole accelerates, it emits a huge amount of energy.

Because the quasars are so bright, they can be seen at great distances. This makes them not only interesting objects of research but also useful as markers for studying the law of Hubble.

Gravity lenses appear when the source of light from an extremely remote object, quasars in this study, faces interference in the galaxy before reaching Earth observers. The final mass of the galaxy is enough to bend the light, similar to the way the glass lens is made. The result is a kind of effect of a "house of mirrors". The image below shows what it looks like. The detection of gravitational lenses is most closely related to Einstein, although it is not observed until 1979.

The image of Hubble's bright red galaxy (LRG) gravitationally distorts the light from a far farther blue galaxy, a technique known as gravitational lensing. Regards: ESA / Hubble & NASA
The image of Hubble's bright red galaxy (LRG) gravitationally distorts the light from a far farther blue galaxy, a technique known as gravitational lensing. Regards: ESA / Hubble & NASA

This study focuses on double quasars. The double quasar, sometimes called double quasar, is not two quasars close to each other, but rather the effect of gravitational lensing. With a double quasar, their light is objective around an intervening galaxy before it reaches the Earth, producing two images of the quasar. No previous study has used them to try to determine the speed of expansion of the universe.

Since the light of the quasar bends around the found galaxy, producing two images of the same quasar, it creates a unique opportunity for observation. The light that creates the individual images of the quasar moves differently to each image. Since the light of the quasar fluctuates, there is a delay between the flicker in each of the two images.

By measuring the delay between oscillation and knowledge of the mass of the galaxy, the team takes the distance between the Earth, the lens galaxy and the quasar. Knowing the red moves of the quasar and the galaxy allowed scientists to assess how quickly the universe expanded.

This study focuses on the dual quasar called SDSS J1206 + 4332, and also relies on Hubble Space Telescope, Gemini and W.M. The Observatories of Keck, as well as the Cosmic Gravity Lens Monitoring or COSMOGRAIL, a network. The team spent several years in daily photos of the double quasar, which gave them very precise measurements of the time between the oscillations. When combined with other data, he gave astronomers one of the best measurements of the Hubble constant.

"The beauty of this measurement is that it is extremely complementary and independent of others," says Thomas Treu, Professor of Physics and Astronomy at UCLA and the senior author of the report.

Image from the paper. The lens galaxy is G0 in the center of the image. A and B is the double quasar SDSS J1206 + 4332. G2 is a triple galaxy and G3 and G4 are other nearby galaxies. Image Credit: The Hubble Space Telescope, Treu et. Al. 2019.

So, how fast is it expanding?

"… The universe is a bit more complicated.


Tommasso Treu, professor of physics and astronomy at UCLA.

The team invented the Hubble Constant value of 72.5 kilometers per second for a mega-parsec. This puts it in line with other measurements that use remote supernovae as standard candles to measure the Hubble constant. But this is about 7% higher than the measurements that rely on the cosmic microwave background to measure it.

This is not the end of the debate about the law of Hubble. There is still this vicious difference between the measurement methods. What does it mean? "If there is a real difference between these values, it means that the universe is a bit more complicated," says Treu. Treu also said one of the measurements, or even the three, was wrong.

The team will retain its quasar-leting measurement method. They are looking for 40 quadruple quasars to hope that they will give them even more accurate measurement of the speed of expansion of the universe.

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