The universe's flashlight into the past just lit up again

March 8, 2021
We might be catching a glimpse back to the start of our universe. (ESO/M. Kornmesser)

We might be catching a glimpse back to the start of our universe. (ESO/M. Kornmesser)

Quasars are like flashlights in the universe that can illuminate a particular moment in history, and astronomers have just found an especially rare one that dates back to nearly 13 billion years ago, possibly offering a peek into the universe's state right after the Big Bang.

About 400,000 years after the Big Bang occurred, the universe remained in a state of complete darkness. But when light started to come about, there were high-energy objects called quasars that lit up the galaxies surrounding them. And results published March 8 in The Astrophysical Journal say a new quasar's light has finally reached Earth. 

"There's a phase change when the universe went from the dark age, where we could not see the light, to the moment when it's transparent," said Chiara Mazzucchelli, a coauthor of the study. "These high redshift quasars are useful because they can be a flashlight for this moment."

These quasars can serve as a portal, taking observers back in time because of the rate at which light travels. Light does not travel instantaneously, even though it may appear so to the human eye. This is why scientists often use the term light-year to explain how fast light travels in one year.

Mazzucchelli, a research fellow at the European Southern Observatory in Chilé, told The Academic Times that the distance of the quasar her team discovered, called P172+18, was detected by observing its redshift. With this method, scientists take advantage of the variations in wavelengths to understand how far away space-borne objects are.

Because red is the longest and final wavelength on the spectrum, an object appears more red as it moves farther and farther away. In contrast, blueshift refers to an object that is approaching.

"There have been quasars found at a higher redshift, which means farther away. It's not a record-breaker in that sense," said Mazzucchelli. "But these quasars, with very powerful radio jets and radio emissions that we can detect, are a very small percentage."

Quasars are often associated with supermassive black holes, but only those that are active can light up the sky. Such quasars are known as having radio jets. Those phenomena accounts for only 10% of observed quasars, making this discovery a profound achievement. 

"It's like these flashlights are lighting up, and we can understand what's happening around them, thanks to their light," Mazzucchelli said. "Even one more of this object, since there are so few of them, can let us know a lot about what was happening in the region at that time."

With a redshift of nearly z=7, it took approximately 13 billion light-years for the light emitted from P172+18 to arrive at the lens of an Earth-based telescope. So, the picture it illuminates will be from 13 billion years ago. Each moment after will fall in accordance with this time-frame. It will give scientists something like a video of the past.

"We saw that this object was a quasar in just seven minutes," Mazzucchelli said — a coincidental but fitting amount of time, given its redshift. "Before this study, redshift 6.1 was found. There's another one that has been identified at 6.4. Having it at almost redshift 7 means it is much earlier than what was known before, not just a small increment." More precisely, the redshift of the newly discovered quasar is z=6.82.

At the center of almost all galaxies, including the Milky Way Galaxy that is home to Earth, supermassive black holes are 1 million and sometimes even 1 billion times the size of the sun. The largest one ever found has a radius of 78 billion miles.

They all have quasars, but the ones with non-dormant quasars have stupendously large radiation emissions and accretion disks around them. The gas and matter from the disks are eaten by the black hole and as this happens, they emit super high-energy fluctuations, giving the surrounding universe tons of light.

"We cannot see the black hole itself because no light can escape it, but the strength of the radiation in wavelengths is so big that we can observe it at the other end of the universe," Mazzucchelli said. "We look for the emission of this gas that's falling into and being eaten by the black hole."

The radiation goes through space's drifting gas, which is then absorbed at different wavelengths depending on the distance of the gas to Earth. By seeing how much of the radiation from the quasar is absorbed by the gas as it moves through it, scientists can understand the temperature, ionization state, amount of stars in formation, nearby galaxy distances and other significant features of the past universe. 

This will add evidence to the mapping of the universe today. 

"We need many of these sources in order to map a large range of directions where this is happening," Mazzucchelli said.

In the future, the team plans to discover more about the environment of P172+18, but hopes to learn how it interacts with the black hole that contains it, too. The researcher remarked that the team "just needed to have a point in the sky to look at." 

She added that, "A challenge we have now is trying to explain how the first supermassive black holes would reach their large solar masses in such a short amount of time," and that "radio jets are thought to help in boosting the growth of these supermassive black holes."

The study, "The Discovery of a Highly Accreting, Radio-loud Quasar at z = 6.82," was published March 8 in The Astrophysical Journal. It was authored by Eduardo Bañados, Jan-Torge Schindler, Irham Taufik Andika, Frederick B. Davies, Bram P. Venemans and Lukas Wenzl, Max Planck Institut für Astronomie; Chiara Mazzucchelli, European Southern Observatory; Emmanuel Momjian and Chris Carilli, National Radio Astronomy Observatory; Anna-Christina Eilers, MIT Kavli Institute for Astrophysics and Space Research; Feige Wang, Xiaohui Fan and Jinyi Yang, University of Arizona; Thomas Connor and Daniel Stern, California Institute of Technology; Aaron J. Barth, University of California, Irvine; Roberto Decarli, Antonio Pensabene, INAF—Osservatorio di Astrofisica e Scienza dello Spazio; Emanuele Paolo Farina, Max Planck Institut für Astrophysik and Joseph F. Hennawi, University of California, Santa Barbara.

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