A Surprise from an Early Universe Monster

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On my more imaginative days, I lament the fact that I do not have a time machine (specifically, a TARDIS.) The good news is, however, that as an astronomer, I can use telescopes as a sort of time machine to look back into the Universe’s past. This view can be murky at times, and a recent Nature paper shows us that we just don’t understand the very young Universe as well as we thought.

As I’ve written previously, I was in South Africa working on a new radio telescope to probe the hydrogen in the early Universe for a few weeks this summer. One of our collaborators back home emailed us excitedly about some new findings that related to our project. A group led by Daniel Mortlock studied a monstrous and very distant quasar which has something interesting to say about its environment.

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The quasar’s name is the ever memorable “ULAS J1120+0641.” Using the Gemini North Telescope, a spectrum of the quasar was taken back in November, confirming a redshift* of 7.085. This means we are seeing the quasar when the Universe was just 770 million years old. (That’s almost 13 BILLION years ago.) This is a time in the Universe about which we know very little, the epoch of reionization.

The epoch of reionization, or EoR, is a time when the earliest galaxies were giving off lots of ultraviolet light. This UV light ionized, or broke apart, the atoms of hydrogen gas that existed between galaxies.

Several telescopes, including the experiment PAPER on which I’m writing my thesis, are searching for this elusive hydrogen signal. The redshift (or time) at which the action happens determines to what frequencies our instruments need to be tuned.

Several quasars at a redshift near 6 (that’s a billion years after the Big Bang) showed signs that they were at the very tail end of reionization. Other studies using the cosmic microwave background implied that reionization took a long time to occur, so we would have to cover a frequency range that went up to a redshift of 12 to catch all of the hydrogen. This new quasar, however, is changing that picture.

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ULAS J1120+0641 looks different from its counterparts at redshift of 6. It shows that the hydrogen medium around it is still 10 percent neutral. This is more neutral hydrogen than astronomers were expecting, so telescopes being built for the EoR experiment need to take the redshift range between 6 and 7 into account and look for something really important there. With many such experiments midway through construction, it will favor those who were already prepared for a bit of “give.”

Of course, this quasar gives just one pierce point over an entire sky, so results are preliminary, and more analyses could even show more neutral gas than the published 10 percent. It’s rather difficult to plan to find something that can’t yet be seen, but the challenge makes it all that much more fun!

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However, I can’t say that I’m too surprised at this result, as a while ago I read a paper that insisted that we didn’t have enough quasars at a redshift of 6 to really say that reionization was done by then. Maybe it extends down to 5… or lower?

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One more fascinating thing about this quasar is the estimated size of the black hole that powers it. It is 2 billion times the mass of our sun. Though that is not unusual for supermassive black holes in the Universe today, this monster only had 770 million years in which to grow to that massive size. At the rate that it is pulling material onto itself, it had to have been born really big to begin with, much larger than the kind of black hole that comes from the death of a massive star. Or, it arose from a merger of many, many much smaller black holes. Either way, as Chris Willcott points out in his commentary in the same issue of Nature as this paper, “t is safe to say that the existence of this quasar will be giving some theorists sleepless nights.”

That’s okay by me. The observers and experimentalists have already lost quite a bit of sleep trying to detect these things!

*Redshift is a measure of how much the light has been “stretched” over cosmic time due to the expanding Universe. So, hydrogen, which normally emits light at 1.4 GHz, can be detected from this epoch in a range between 100 and 200 MHz. (Yes, that’s right near the FM radio band. Yay for us!) In this way, redshift can be correlated with the age of the universe, where a higher redshift indicates and earlier epoch.

Thanks to Chris Carilli for bringing this work to our attention while we were running around in the desert on the other side of the planet! I have linked to the preprints of these papers in the text, and the final papers can be found (behind paywalls) here, here, and here

Image: Artist’s conception of a bright quasar at the center of a galaxy. Credit: NASA