Gemini: cosmic telescope zooms in on beginning of time

Before the cosmos reached its billionth birthday, some of the very first cosmic light began a long journey through the expanding universe. One particular beam of light, from an energetic source called a quasar, serendipitously passed near an intervening galaxy, whose gravity bent and magnified the quasar's light and refocused it in our direction, allowing telescopes like Gemini North to probe the quasar in great detail.

"If it weren't for this makeshift cosmic telescope, the quasar's light would appear about 50 times dimmer," said Xiaohui Fan of the University of Arizona, who led the study. "This discovery demonstrates that strongly gravitationally lensed quasars do exist despite the fact that we've been looking for over 20 years and not found any others this far back in time."

The Gemini observations provided key pieces of the puzzle by filling a critical hole in the data. The Gemini North telescope on Maunakea, Hawaii, utilized the Gemini Near-InfraRed Spectrograph (GNIRS) to dissect a significant swath of the infrared part of the light's spectrum. The Gemini data contained the telltale signature of magnesium, which is critical for determining how far back in time we are looking. T

he Gemini observations also led to a determination of the mass of the black hole powering the quasar. "When we combined the Gemini data with observations from multiple observatories on Maunakea, the Hubble Space Telescope, and other observatories around the world, we were able to paint a complete picture of the quasar and the intervening galaxy," said Feige Wang of the University of California, Santa Barbara, who is a member of the discovery team.

That picture reveals that the quasar is located extremely far back in time and space - shortly after what is known as the Epoch of Reionization - when the very first light emerged from the Big Bang. "This is one of the first sources to shine as the universe emerged from the cosmic dark ages," said Jinyi Yang of the University of Arizona, another member of the discovery team. "Prior to this, no stars, quasars, or galaxies had been formed, until objects like this appeared like candles in the dark."

The foreground galaxy that enhances our view of the quasar is especially dim, which is extremely fortuitous. "If this galaxy were much brighter, we wouldn't have been able to differentiate it from the quasar," explained Fan, adding that this finding will change the way astronomers look for lensed quasars in the future and could significantly increase the number of lensed quasar discoveries. However, as Fan suggested, "We don't expect to find many quasars brighter than this one in the whole observable universe."

The intense brilliance of the quasar also suggests that it is fueled by a supermassive black hole at the heart of a young forming galaxy. The broad appearance of the magnesium fingerprint captured by Gemini also allowed astronomers to measure the mass of the quasar's supermassive black hole at 700 million times that of the Sun. The supermassive black hole is most likely surrounded by a sizable flattened disk of dust and gas. This torus of matter - known as an accretion disk - most likely continually spirals inward to feed the black hole powerhouse.

Observations at submillimeter wavelengths with the James Clerk Maxwell Telescope on Maunakea suggest that the black hole is not only accreting gas but may be triggering star birth at a prodigious rate - which appears to be up to 10,000 stars per year; by comparison, our Milky Way Galaxy makes one star per year. However, because of the boosting effect of gravitational lensing, the actual rate of star formation could be much lower.

Quasars are extremely energetic sources powered by huge black holes thought to have resided in the very first galaxies to form in the universe. Because of their brightness and distance, quasars provide a unique glimpse into the conditions in the early universe.

This quasar, known as j043947.08+163415.7 (j0439+1634 for short), has a redshift of 6.51, which translates to a distance of 12.8 billion light-years, and appears to shine with a combined light of about 600 trillion Suns, boosted by the gravitational lensing magnification. The foreground galaxy that bent the quasar's light is about half that distance away, at a mere 6 billion light-years from us.

Fan's team selected j0439+1634 as a very distant quasar candidate based on optical data from several sources: the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1; operated by the University of Hawaii's Institute for Astronomy), the United Kingdom Infrared Telescope Hemisphere Survey (conducted on Maunakea, Hawaii), and NASA's Wide-field Infrared Survey Explorer (WISE) space telescope archive.

The first follow-up spectroscopic observations, conducted at the Multi-Mirror Telescope in Arizona, confirmed the object as a high-redshift quasar. Subsequent observations with the Gemini North and Keck I telescopes in Hawaii confirmed the MMT's finding and led to Gemini's detection of the crucial magnesium fingerprint - the key to nailing down the quasar's fantastic distance.

However, the foreground lensing galaxy and the quasar appear so close that it is impossible to separate them with images taken from the ground due to blurring of the Earth's atmosphere. It took the exquisitely sharp images by the Hubble Space Telescope to reveal that the quasar image is split into three components by a faint lensing galaxy.

The quasar is ripe for future scrutiny. Astronomers also plan to use the Atacama Large Millimeter/submillimeter Array, and eventually NASA's James Webb Space Telescope, to look within 150 light-years of the black hole and directly detect the influence of the gravity from black hole on gas motion and star formation in its vicinity. Any future discoveries of very distant quasars like j0439+1634 will continue to teach astronomers about the chemical environment and the growth of massive black holes in our early universe.

Research Report: "The Discovery of a Gravitationally Lensed Quasar at z = 6.51," Xiaohui Fan et al., 2019, to appear in Astrophysical Journal Letters

Related Links
Gemini Observatory
Understanding Time and Space

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