We live in a time when our telescopes can look back to almost the beginning of the universe. That includes the most distant reaches of the cosmos, and, of course, everything in between. Even though astronomers have a good idea of the different categories of objects in the universe, they’re still learning about the details. Take quasars, for example. They exist throughout the universe and appear to have been most active earlier in cosmic history. Understanding them has taken decades, and there is still a LOT to learn about these distant cosmic objects.
The name “quasar” comes from the term “quasi-stellar object”. They caught astronomers’ attention back in the 1950s. That’s when the first ones were detected as strong radio-frequency emitters. Images taken later on showed dim, star-like objects that were the sources of the strong radio emissions. Yet, spectroscopic studies of the light emitted showed that these dim things lay at huge distances from Earth. What could be that strong in radio, show up as a dim star, and be so far away? It was a challenge for astronomers to explain them.
Today, we know quite a bit more about quasars. Their activity comes from the gobbling action of central supermassive black hole embedded in massive galaxies. Yes, black holes are the “engines” of quasars. Astronomers estimate that 50,000 exist and more will be discovered as they scan the sky.
Distance is Important
Recently, astronomers using the Gemini Telescope on Mauna Kea in Hawai’i found Poniua’ena, in a sky survey. Then, they followed up with spectroscopic studies using the Keck telescope. Poniua’ena is a Hawai’ian name. It means “unseen spinning source of creation, surrounded with brilliance.” (The catalog number is J1007+2115.) And, yes, it’s incredibly brilliant and, at just over 13 billion light-years, is nearly as far away as ULAS J1342+0928.
The most known distant quasar, called ULAS J1342+0928 is the current record-holder, at just over 13 billion light-years. The universe itself currently is somewhere around 13.7 billion years old. ULAS (for short) was born during a time when the first stars and galaxies were coalescing (the so-called “epoch of reionization” (EOR). So, that makes this quasar and Poniua’ena very old. They formed when the universe was very young. And, early quasars raise questions about their black holes. How could they grow so large so quickly to create quasars only a few hundred million years after the universe was born?
Quasars and the Epoch of Reionization
The EOR is, itself a fascinating challenge to study. Its distant, its objects are mostly dim, and astronomers are still watching for its earliest “ignition”. The birth of stars and galaxies started during the EOR, and about 400 million years into this period of cosmic history, the first black holes “seeds” may have begun to form. Interestingly, black holes are the central engines for quasars, but they are far more massive than the tiny ones that existed “way back when”.
Like other quasars, ULAS J1342+0928 and Poniua’ena get their power from the black holes at the hearts of their host galaxies. For ULAS, the black hole has about 800 million times the mass of the Sun. Poniua’ena’s is 1.5 billion solar masses.
Activities in the superheated region around the black holes (including jets) are what make the quasars look so bright. As material spins down into the black hole, it gets heated by friction, and also by the action of powerful magnetic fields. That heating produces radiation in the form of light across the electromagnetic spectrum. Some material escapes through powerful jets that stream from the region of the black hole. That, too, emits radiation. It’s a busy, hot, and lethal environment.
Looking for Quasars
So, are there other quasars just as distant as ULAS J1342+0928? and Poniua’ena? That’s the question astronomers want to answer as they survey the sky with various instruments that can detect the light and other radiation emanating from quasars. Since quasars appear early in cosmic time, they play some role in the history and evolution of the universe. The exact nature of that role remains to be understood. To even being to figure it out, astronomers have to do wide-area sky surveys to find these quasars, which is like searching for the proverbial needle in a haystack.
Forming Quasars
Obviously, to get to be a quasar, a massive galaxy needs a supermassive black hole at its heart. Early on in its formation, the galaxy may have a fairly small black hole in the core. But, to shine brightly across billions of light-years, the black hole has to become more massive. Since it grows by gathering more and mass into itself, eventually it becomes a supermassive black hole that powers the quasar. But, that raises an interesting conundrum.
Making a supermassive black hole takes a long time. And, for a quasar to exist when the first stars were forming after the birth of the universe, that means its supermassive black hole “engine” had to grow fairly fast. So, one big question about these early, distant quasars is: how did the universe produce such massive quasar engines so quickly?
Quasar Poniua’ena’s Early Existence
For Poniua’ena, that means its black hole had to start as a fairly massive black hole “seed” a hundred million years after the Big Bang occurred. That’s sort of like expecting a newborn baby to write the complete works of Shakespeare or formulate a new language only a few months after it is born. The existence of such massive black holes in the hearts of galaxies so soon after the universe was born challenges current theories about how they form.
The discovery and study of very distant quasars such as Poniua‘ena and ULAS J1342+0928 shed insight into the early universe. Both they and their massive galaxy hosts formed deep in the Epoch of Reionization. How and why did they form so early? What processes are at work to enable such massive objects to exist so early? Are there earlier quasars than these? The answers to all these questions will (if you’ll pardon the pun) shed light on the earliest events that we can possibly observe in our universe.