The masses of the observed black holes in such an Early-Universe is larger than expected, posing the question: "How could these black holes grow to be so large when the universe was so young?"
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New images from the James Webb Space Telescope have revealed, for the first time, starlight from two massive galaxies hosting actively growing black holes – quasars – seen less than a billion years after the Big Bang. A new study in Nature this week finds the black holes have masses close to a billion times that of the Sun, and the host galaxy masses are almost one hundred times larger, a ratio similar to what is found in the more recent universe. A powerful combination of the Subaru Telescope and the JWST has paved a new path to study the distant universe.   

The existence of such massive black holes in the distant universe has created more questions than answers for astrophysicists. How could these black holes grow to be so large when the universe was so young? Even more puzzling, observations in the local universe show a clear relation between the mass of supermassive black holes and the much larger galaxies in which they reside. The galaxies and the black holes have completely different sizes, so which came first: the black holes or the galaxies?  This is a “chicken-or-egg” problem on a cosmic scale.

An international team of researchers, led by Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Project Researcher Xuheng Ding and Professor John Silverman, and Peking University Kavli Institute for Astronomy and Astrophysics (PKU-KIAA) Kavli Astrophysics Fellow Masafusa Onoue have started to answer this question with the James Webb Space Telescope (JWST), launched in December 2021. Studying the relation between host galaxies and black holes in the early universe allows scientists to watch their formation, and see how they are related to one another.  

"The central black hole acts on its hosting galaxy in some way to produce the observed relation. Understanding this mechanism is a hot topic and this paper will bring us closer to doing so", says Dr. Kazushi Iwasawa, researcher of the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institute of Space Studies of Catalonia (IEEC) and one of the core members of the team that discovered the early-universe quasars.

Quasars are luminous, while their host galaxies are faint, which has made it challenging for researchers to detect the dim light of the galaxy in the glare of the quasar, especially at great distances.  Before the JWST, the Hubble Space Telescope was able to detect host galaxies of luminous quasars when the universe was just under 3 billion years old, but no younger. 

The superb sensitivity and the ultra-sharp images of the JWST at infrared wavelengths finally allowed researchers to push these studies to the time when the quasars and galaxies first formed.  Just a few months after JWST started regular operations, the team observed two quasars, HSC J2236+0032 and HSC J2255+0251, at redshifts 6.40 and 6.34 when the universe was approximately 860 million years old. These two quasars were discovered in a deep survey program of the 8.2m-Subaru Telescope on the summit of Maunakea in Hawai’i.  The relatively low luminosities of these quasars made them prime targets for measurement of the host galaxy properties, and the successful detection of the hosts represents the earliest epoch to date at which starlight has been detected in a quasar.  

The images of the two quasars were taken at infrared wavelengths of 3.56 and 1.50 micron with JWST’s NIRCam instrument, and the host galaxies became apparent after carefully modeling and subtracting glare from the accreting black holes. The stellar signature of the host galaxy was also seen in a spectrum taken by JWST’s NIRSPEC for J2236+0032, further supporting the detection of the host galaxy.

Analyses of the host galaxy photometry found that these two quasar host galaxies are massive, measuring 130 and 34 billion times the mass of the Sun, respectively. Measuring the speed of the turbulent gas in the vicinity of the quasars from the NIRSPEC spectra suggest that the black holes that power them are also massive, measuring 1.4 and 0.2 billion times the mass of the Sun. The ratio of the black hole mass to host galaxy mass is similar to those of galaxies in the more recent past, suggesting that the relationship between black holes and their hosts was already in place 860 million years after the Big Bang.  

Ding, Silverman, Onoue and their colleagues will continue this study with a larger sample using scheduled Cycle 1 JWST observations, which will then further constrain models for the coevolution of black holes and their host galaxies. The team recently learned that they have been awarded additional time for JWST in its next cycle to study the host galaxy of J2236+0032 in much more detail.  

Details of this study were published in Nature on June 28.

Ding, Onoue, Silverman et al.
Figure 1: JWST NIRCam 3.6 μm image of HSC J2236+0032. The zoom-out image, the quasar image, and the host galaxy image after subtracting the quasar light (from left to right). The image scale in light years is indicated in each panel. Credit: Ding, Onoue, Silverman et al.

Paper details
Detection of stellar light from quasar host galaxies at redshifts above 6
DOI: 10.1038/s41586-023-06345-5

Related links

Astronomers Discover 83 Supermassive Black Holes in the Early Universe (Subaru Telescope press release on March 13, 2019) 

Expressing the distance to remote objects

About the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP)

The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is a three-layered imaging survey, using the Hyper Suprime-Cam on the 8.2m Subaru Telescope on the summit of Maunakea in Hawai’i, aimed at addressing some of the most important and outstanding questions in astronomy today, including the nature of dark matter and dark energy. 

The survey consisted of 330 nights of observation time on the Subaru Telescope between 2014 and 2021, mapping out an area of more than 1100 square degrees, or 5,500 times the area of the Moon, of the deep universe. 

The HSC-SSP is led by the astronomical communities of Japan and Taiwan, and Princeton University.