Quasar Discovery Challenges Black Hole Theories — Dare to Know
A quasar discovery suggests that stars existed much earlier than scientists thought. Find out why this challenges our understanding of black hold formation.
The first time I heard the word “quasar” was in the late 60s. Motorola brought out a new line of televisions sets that used transistors instead of the old vacuum tubes.
A big selling point was that these new models had their “works in a drawer.” That made them more accessible to service, which was something my parents’ generation needed to do quite often with TVs of that vintage.
As I’ve shared in these pages before, I grew up in the Space Age. We viewed everything through the lens of the space race and the moon landings.
We Viewed Everything Through the Lens of the Space Race
NASA relied heavily on transistors in its space program because they were compact and more reliable than older electronic systems. One way that NASA sold the space program to the public was by emphasizing the spin-off benefits in new technology that their research and development fostered.
Astronomer Hong-Yee Chiu coined the term quasar as an abbreviation for a new phenomenon called a quasi-stellar radio source in 1964. So naturally, the word quickly became an electronics brand.
The real quasars out in space are puzzling. Astronomers started using radio telescopes in the 1950s, and they started picking up unusual objects.
Radio Telescopes Started Picking Up Unusual Objects
The new phenomena emitted signals across many frequencies. Yet, when they looked for them with optical telescopes, either they couldn’t find them, or the object looked faint and non-descript.
Scientists can tell what objects are made of by looking at their spectrum of light. That raised even more questions.
Their brightness often changed very quickly, in the visible light range and even more rapidly at the X-ray level. At least that provided a clue to their size, which seemed to be not much bigger than the solar system.
So Much Powerful Energy in a Tight Space
That brought up another question. How could so much powerful energy be packed into such a tight space? Since they were star-like objects that emitted a wide range of radio frequencies, they got the name quasi-stellar radio source, quasar for short.
Throughout the sixties, astronomers made hundreds more quasar discoveries. In one case, astronomer John Bolton worked out that the moon would block a radio source called 3C 273 on five different occasions.
On one of those occasions, Cyril Hazard partnered with John Bolton to make some measurements using the Parkes Radio Telescope. Astronomer Maarten Schmidt worked from those measurements and located the object visually with the Hale Telescope on Mount Palomar.
Hydrogen Spectrum Redshifted by 15.8 Percent
The same odd spectrum turned up, and Schmidt concluded that it was an ordinary hydrogen spectrum but redshifted by 15.8%. Schmidt thought about redshifts and realized that the overall expansion of the universe was what usually caused them.
That would mean that quasars were much further away than anyone had imagined. They would also have to be immensely bright and energetic.
Schmidt decided that they must be the central cores of distant galaxies, or at least something very remote and extremely energetic. That still didn’t explain the reason for their intense energy density.
Central Cores of Distant Galaxies
A lot of fanciful explanations arose through the 60s and 70s until cosmologists finally hit on the right answer. A quasar forms when a newly formed star and the disk that usually forms its solar system get trapped in a supermassive black hole.
As scientists have learned more about black holes, they’ve determined that quasars exist in the black holes at the centres of distant galaxies. They’re so bright, and the galaxies are so remote that the quasar outshines the galaxy, hiding it.
Quasars are in the news this week because scientists from the University of California at Santa Barbara made the second most distant quasar discovery ever found. It’s about 13 billion light-years away, which means it existed not long after the universe began with the Big Bang.
Existed Not Long After the Universe Began
The journal Astrophysical Letters will be publishing their results. The research team has given the new quasar a Hawaiian name.
They’re calling their quasar discovery Poniuaena. It’s hard to translate elegantly, but it means “unseen spinning source of creation, surrounded with brilliance.” No one has ever given a quasar a Hawaiian name before.
There’s a reason for that. As team leader Joe Hennawi explains, “Through University of California Observatories, we have privileged access to the Keck telescopes on the summit of Mauna Kea, which allowed us to obtain high-quality data on this object shortly after it was discovered using the Gemini telescope.”
Most Luminous Objects in the Universe
Professor Hennawi explained our current understanding of quasars this way “They are the most luminous objects in the Universe, outshining their host galaxies by factors of more than a hundred.”
Today’s cosmologists are trying to work out how long quasars have been around. They also want to learn more about their role in the development of the universe.
Like many of today’s deep-sky researchers, the team found Poniuaena by poring through the large area sky surveys modern telescopes generate. They then managed to pinpoint it visually using the Keck and Gemini telescopes.
1.5 Billion Times More Massive Than the Sun
Poniuaena is twice the size of the most distant quasar of all. For perspective, it’s also about 1.5 billion times more massive than the sun.
Although it’s only the second-most distant quasar discovery, it has another claim to fame. Team member Jinyi Yang from the University of Arizona explained, “Poniuaena is the most distant object known in the universe hosting a black hole exceeding one billion solar masses.”
This quasar discovery and the most distant quasar of all are both about 13 billion light-years away. Since we look back in time when we look out into space, that makes them both more than 13 billion years old.
Both Quasars More than 13 Billion Years Old
The Big Bang took place about 13.8 billion years ago. The proximity of these two dates is puzzling for cosmologists because it’s inconsistent with their current understanding of black hole formation and growth.
Physicists believe that supermassive black holes form out of the remnants of massive stars after they die. Scientists call these massive dead stars seed holes. The seed hole’s gravity gradually draws in more matter, eventually building up to join the supermassive category of black holes.
The riddle that Poniuaena and even more distant rival pose is that cosmologists didn’t think that massive stars formed that early. The seed hole for Poniuaena must have had the mass of 10,000 suns. It also must have existed just 100 million years after the Big Bang.
Existed Just 100 Million Years After the Big Bang
Team member Xiaohui Fan, at the University of Arizona, asked, “How can the universe produce such a massive black hole so early in its history?” He pointed out that, “This discovery presents the biggest challenge yet for the theory of black hole formation and growth in the early universe.”
Up until now, the standard model has said that stars began to form during the Epoch of Reionization. Cosmologists believed that the epoch began about 400 million years after the Big Bang.
Yet, based on current theories, the star from which Poniuaena arose must have already existed 300 million years before that. Professor Hennawi waxed poetic about the discovery and the puzzle.
“Poniuaena Acts Like a Cosmic Lighthouse”
“Poniuaena acts like a cosmic lighthouse. As its light travels the long journey towards Earth, its spectrum is altered by diffuse gas in the intergalactic medium, which allowed us to pinpoint when the Epoch of Reionization occurred.”
Plans are in the works to find ways to get to the bottom of the mystery posed by this quasar discovery by finding more quasars. These plans include new machine learning applications to help sift through the star surveys, the Euclid Satellite and the James Webb Telescope.
Professor Hennawi concluded by saying, “With a large statistical sample of these objects, we will be able to construct a precise timeline of the reionization epoch as well as shed more light on the black hole growth puzzle.”
We always have more to learn if we dare to know.
Beacon from the Early Universe
Poniuaena: A Luminous z=7.5 Quasar Hosting a 1.5 Billion Solar Mass Black Hole
Newborn Stars Bringing Forth Solar Systems
Are Supermassive Black Holes Collapsed Stars?
Three Black Holes Colliding in Galaxy’s Core
Originally published at https://daretoknow.ca on July 7, 2020.