Hubble has discovered double quasars living in the core of galaxies.
Surendra Uikey
This artist’s concept illustrates the remarkable glow of two quasars residing in the hearts of two merging galaxies,The gravitational tug-of-war between the two galaxies triggers a tempest of star formation. Quasars are brilliant beacons of intense light from the depths of faraway galaxies and are powered by supermassive black holes eating up matter falling into them. This feeding process releases a vast amount of radiation so powerful, it can outshine the total light emitted from billions of stars in its host galaxy. In the next few tens of millions of years, both black holes and their galaxies will merge, resulting in the combination of the pair of quasars into an even larger black hole.
The early universe was a wild and chaotic place, with galaxies colliding and merging together,This activity was recently discovered by astronomers observing through NASA’s Hubble Space Telescope and other instruments, and revealed two quasars, held together by gravity, both housed within two merging galaxies.Finding close binary quasars is a relatively new area of research that has just developed in the past 10 to 15 years. This breakthrough was made possible thanks to the advancement of today’s powerful new observatories which allowed astronomers to identify instances where two quasars were active at the same time and close enough to be considered close binary quasars.
The discovery of a double quasar at such an early time in the universe is incredibly exciting, according to Yu-Ching Chen, a graduate student of the University of Illinois at Urbana-Champaign and lead author of this study. Double quasars are rarely seen in the universe, and this find is unprecedented. It offers an opportunity to learn more about the early stages of the universe and the physics that governs it. It also provides insight into how supermassive black holes form and the role they play in the evolution of galaxies.
The merging of smaller galaxies to form larger structures is becoming increasingly accepted as a way for large galaxies to be built. In this process, pairs of supermassive black holes should also be formed. According to Chen, understanding this progenitor population of black holes will eventually help us figure out the origin of these supermassive black holes in the early universe, and how regular these kinds of mergers may have been. Xin Liu from the University of Illinois at Urbana-Champaign further adds to this revelation by saying that their study has uncovered the unique beginnings of a binary quasar population, and now they possess a method to spot double quasars that are present within a single galaxy. All of this leads us to one conclusion: mergers play an important role in the formation of large galaxies and supermassive black holes.
A pair of quasars existed at that time in the 3 billion year old universe.
The Hubble Space Telescope photograph of a pair of quasars existing when the universe was just 3 billion years old is an incredible sight. Embedded within a pair of colliding galaxies, the quasars are separated by less than the size of a single galaxy. Quasars are extremely powerful, and are fueled by voracious supermassive black holes that blast out energy as they consume gas, dust, and whatever else happens to be within their gravitational grasp. Eventually the black holes will merge, creating an even more powerful source of energy. This Hubble Space Telescope photograph is a glimpse into the distant past, and shows us the immense power of quasars.
This needle-in-haystack search required the combined power of some of the most powerful space observatories in the world. NASA’s Hubble Space Telescope and the W.M. Keck Observatories in Hawaii provided multi-wavelength observations, while NSF’s Karl G. Jansky Very Large Array in New Mexico and NASA’s Chandra X-ray Observatory contributed to understanding the dynamic duo. Additionally, ESA’s Gaia space observatory helped identify this double quasar in the first place. According to Chen, Hubble’s sensitivity and resolution provided pictures that definitively rule out other possibilities, thus confirming that this double quasar is indeed a genuine pair of supermassive black holes, rather than two images formed by a foreground gravitational lens. Hubble also revealed a tidal feature from the merging of two galaxies, with gravity distorting their shapes into two tails of stars.
The search for double quasars necessitates a powerful tool – one that is capable of detecting the subtle jiggle created by the alternating brightness of the quasar pair. Unfortunately, Hubble’s sharp resolution alone isn’t enough for this task. That’s why the researchers enlisted the help of Gaia, which launched in 2013. Gaia measures the positions, distances, and motions of celestial objects with high precision and its huge database was used to search for quasars that mimic the apparent motion of nearby stars. These quasars appear as single objects in Gaia data due to their closeness to each other. However, Gaia can pick up a subtle, unexpected jiggle that mimics an apparent change in position of some quasars it observes. This jiggle is not evidence of any measurable movement in space; it is simply a result of random fluctuations in light when each member of the quasar pair varies in brightness over time intervals between days and months, depending on its black hole’s feeding schedule. This alternating brightness is similar to seeing a railroad crossing signal from a distance: as the two lights on both sides of the stationary signal alternately flash, it gives an illusion of jiggling.
With the help of the Keck telescope, astronomers were able to determine whether a distant quasar was actually two, or just an illusion created by a foreground galaxy. This is a challenge, as gravity warps space like a funhouse mirror. As Hubble peers into the distant past, the double quasar no longer exists and has likely morphed into a giant elliptical galaxy, similar to those seen in the local universe. This galaxy likely houses a supermassive black hole that is the merged result of one or more quasars over billions of years. An example of this is in M87, which has a monstrous black hole weighing 6.5 billion times the mass of our Sun. Thus, it can be seen how fascinating and complex the universe really is.
The upcoming NASA Nancy Grace Roman Space Telescope is proving to be an ideal tool for hunting binary quasars due to its impressive visual acuity matching that of Hubble. Hubble has been used to painstakingly take data for individual targets, a laborious process. However, the ultra-wide angle infrared view of the universe offered by Roman is 200 times larger than Hubble’s and thus offers researchers an incredible amount of new data to work with. According to Liu, this massive increase in the amount of data available will lead to “huge improvements in this research area,” as Roman is more than capable of identifying binary quasar systems which would have been nearly impossible with Hubble. The Roman telescope will certainly revolutionize quasar research and open up a host of new possibilities.
