Astronomers using the NASA/ESA Hubble Space Telescope have spotted GNz7q, a black hole that existed only 750 million years after the Big Bang, in one of the best-studied areas of the night sky, the Great Observatories Origins Deep Survey-North (GOODS-North) field.
An artist’s impression of a supermassive black hole that is inside the dust-shrouded core of a starburst galaxy. Image credit: NASA / ESA / N. Bartmann.
Rapidly growing black holes in dusty, early star-forming galaxies are predicted by theories and computer simulations, but had not been observed until now.
“Our analysis suggests that GNz7q is the first example of a rapidly growing black hole in the dusty core of a starburst galaxy at an epoch close to the earliest supermassive black hole known in the Universe,” said Dr. Seiji Fujimoto, an astronomer with the Niels Bohr Institute at the University of Copenhagen.
“The object’s properties across the electromagnetic spectrum are in excellent agreement with predictions from theoretical simulations.”
One of the outstanding mysteries in astronomy today is: how did supermassive black holes, weighing millions to billions of times the mass of the Sun, get to be so huge so fast?
Current theories predict that supermassive black holes begin their lives in the dust-shrouded cores of starburst galaxies before expelling the surrounding gas and dust and emerging as extremely luminous quasars.
While extremely rare, both these dusty starburst galaxies and luminous quasars have been detected in the early Universe.
Dr. Fujimoto and colleagues believe that GNz7q could be a missing link between these two classes of objects.
GNz7q has exactly both aspects of the dusty starburst galaxy and the quasar, where the quasar light shows the dust reddened color.
Also, GNz7q lacks various features that are usually observed in typical, very luminous quasars (corresponding to the emission from the accretion disk of the supermassive black hole), which is most likely explained that the central black hole in GN7q is still in a young and less massive phase.
These properties perfectly match with the young, transition phase quasar that has been predicted in simulations, but never identified at similarly high-redshift Universe as the very luminous quasars so far identified up to a redshift of 7.6.
“GNz7q provides a direct connection between these two rare populations and provides a new avenue toward understanding the rapid growth of supermassive black holes in the early days of the Universe,” Dr. Fujimoto said.
“Our discovery provides an example of precursors to the supermassive black holes we observe at later epochs.”
GNz7q is the red dot in the center of the GOODS-North image. Image credit: NASA / ESA / Garth Illingworth, UC Santa Cruz / Pascal Oesch, UC Santa Cruz & Yale / Rychard Bouwens, LEI / I. Labbe, LEI / Cosmic Dawn Center / Niels Bohr Institute, University of Copenhagen.
While other interpretations of the team’s data cannot be completely ruled out, the observed properties of GNz7q are in strong agreement with theoretical predictions.
GNz7q’s host galaxy is forming stars at the rate of 1,600 solar masses per year, and GNz7q itself appears bright at UV wavelengths but very faint at X-ray wavelengths.
Generally, the accretion disk of a massive black hole should be very bright in both UV and X-ray light.
But this time, although the team detected UV light with Hubble, X-ray light was invisible even with one of the deepest X-ray datasets.
These results suggest that the core of the accretion disk, where X-rays originate, is still obscured; while the outer part of the accretion disk, where UV light originates, is becoming unobscured.
This interpretation is that GNz7q is a rapidly growing black hole still obscured by the dusty core of its star-forming host galaxy.
“GNz7q is a unique discovery that was found just at the center of a famous, well-studied sky field — it shows that big discoveries can often be hidden just in front of you,” said Dr. Gabriel Brammer, also from the Niels Bohr Institute at the University of Copenhagen.
“It’s unlikely that discovering GNz7q within the relatively small GOODS-North survey area was just ‘dumb luck,’ but rather that the prevalence of such sources may in fact be significantly higher than previously thought.”
The discovery is reported in a paper in the journal Nature.
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S. Fujimoto et al. 2022. A dusty compact object bridging galaxies and quasars at cosmic dawn. Nature 604, 261-265; doi: 10.1038/s41586-022-04454-1
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