The early days of our Universe, which is approximately 13.8 billion years old, were a very rough time. Constant galactic cataclysms and upheavals were the norms. Now astronomers have spotted a distant object: a rapidly growing black hole dubbed GNz7q, which is thought to be a supermassive black hole born fairly close to the Big Bang. Studying such an object, whose traits have been described by NASA as "a crucial "missing link" between young star-forming galaxies and the first supermassive black holes," could bring astronomers invaluable insights into how our universe came to be what it is today.
GNz7q, the object identified by the science team, came into existence during the period known as “Cosmic Dawn,” some 750 million years after the Big Bang, the leading theory for the starting point of our universe.
The scientists involved in the study hail from the Cosmic Dawn Center (DAWN), a collaborative project between the Niels Bohr Institute, the University of Copenhagen, and the Technical University of Denmark. As they explain in their paper, “A dusty compact object bridging galaxies and quasars at cosmic dawn,” published in Nature, the astronomers knew that simulations predicted objects like the one they found to be possible, but this is the first time such an object has actually been located. "Simulations indicate an evolutionary sequence of dust-reddened quasars emerging from heavily dust-obscured starbursts that then transition to unobscured luminous quasars by expelling gas and dust," write the researchers in their paper.
The data they used to locate GNz7q came from the Hubble Space Telescope, managed jointly by ESA and NASA. The scientists looked back in time as much as they did in space, discovering phenomena from much earlier days in the history of the cosmos, as light and radiation have to travel great distances to reach us.
Finding the missing link
Seiji Fujimoto, a postdoctoral fellow at the Niels Bohr Institute, University of Copenhagen, and the paper's lead author, believes the object they found provides a sought-after missing stage in the evolution of supermassive black holes. “The discovered object connects two rare populations of celestial objects, namely dusty starbursts and luminous quasars, and thereby provides a new avenue toward understanding the rapid growth of supermassive black holes in the early universe,” explained Fujimoto.
According to prevailing theories, supermassive black holes are predicted to form in the dusty cores of rapidly star-forming "starburst" galaxies until emerging as highly luminous quasars. Starburst galaxies and luminous quasars have both been detected in the early universe. But until now, there was no evidence linking them.
GNz7q lies somewhere in between such a starburst galaxy and a quasar. The scientists believe that GNz7q was born in a galaxy that forms stars at an extremely high rate of around 1,600 solar masses per year, much faster than in our Milky Way galaxy. This process also leads to the creation and heating of cosmic dust, which glows in infrared.
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.
Quasars are astronomical objects of extremely high luminosity, with the brightest of them outshining all the stars in the galaxies in whose centers they can be located. When the gas heads towards the black hole, friction heats it up leading to a tremendous amount of luminosity.
“Although luminous quasars had already been found even at the earliest epochs of the universe, the transition phase of rapid growth of both the black hole and its star-bursting host had not been found at similar epochs,“ elaborated Associate Professor Gabriel Brammer, Niels Bohr Institute, adding “Moreover, the observed properties are in excellent agreement with the theoretical simulations and suggest that GNz7q is the first example of the transitioning, rapid growth phase of black holes at the dusty star core, an ancestor of the later supermassive black hole.”
The research team made their find in the Great Observatories Origins Deep Survey-North (GOODS-North) sky field that has already been studied quite closely. The discovery was made possible thanks to a much more detailed multi-wavelength dataset. Further high-resolution surveys will likely help spot more objects like GNz7q, with special hope placed on the recently-launched NASA/ESA/CSA James Webb Space Telescope, humanity’s most powerful instrument for peering far into space.
“Fully characterizing these objects and probing their evolution and underlying physics in much greater detail will become possible with the James Webb Telescope. Once in regular operation, Webb will have the power to decisively determine how common these rapidly growing black holes truly are,” Seiji Fujimoto shared in a press release.
Why is the James Webb Telescope such a perfect tool for this research? As NASA explains, the JWST, or Webb as it's sometimes called, is actually an orbiting infrared observatory. Its stated purpose is to "complement and extend the discoveries of the Hubble Space Telescope," which it will accomplish thanks to longer wavelength coverage and remarkable sensitivity. Seeing longer wavelengths helps Webb to "look much closer to the beginning of time and to hunt for the unobserved formation of the first galaxies," describes NASA. The telescope can also peek into dust clouds where stars and planetary systems are being formed.