Figure:
SDSS J141637.44+003352.2, a dual quasar at a distance for which the
light reaching us was emitted 4.6 billion years ago. The two quasars are
13,000 light years apart on the sky, placing them near the center of a
single massive galaxy that appears to be part of a group, as shown by
the neighboring galaxies in the left panel. In the lower panels, optical
spectroscopy has revealed broad emission lines as-sociated with each of
the two quasars, indicating that the gas is moving at thou-sands of
kilometers per second in the vicinity of two distinct supermassive black
holes. The two quasars are different colors, due to different amounts
of dust in front of them. (Credit：Silverman et al.)In our dynamically evolving Universe, galaxies occasionally experience collisions and mergers with a neighboring galaxy. These events can be dramatic, causing the birth of new stars, and the rapid feeding of the supermassive black hole that resides in each galaxy. It’s understood that these enormous black holes have masses millions to billions times larger than our Sun and exist in the center of all massive galaxies. As material swirls around the black hole, it is heated to high temperatures, releas-ing so much light that it can outshine its host galaxy. Astronomers refer to this phe-nomenon as a quasar.
Simulations of galaxy mergers demonstrate that sometimes quasar activity occurs at the center of both galaxies concurrently as they undergo a cosmic dance. Such a merging pair will arise as a pair of luminous “dual” quasars. While astronomers have previously found a modest number of luminous quasar pairs, they are rare, much more so than the simulations predict. The difficulty has been not having observa-tions with both the ability to separate the light from the two quasars in close prox-imity and wide enough area coverage of the sky to catch these rare events in suffi-cient numbers.
To overcome these challenges, astronomers are
taking advantage of a sensitive wide survey of the sky, using the Hyper
Suprime-Cam (HSC) camera on the Subaru Tele-scope, to search for dual
quasars. “To make our job easier, we started by looking at the 34,476
known quasars from the Sloan Digital Sky Survey with HSC imaging to
identify those having two (or more) distinct centers,” explains lead
researcher John Silverman, of the Kavli Institute for the Physics and
Mathematics of the Universe. “Honestly, we didn’t start out looking for
dual quasars. We were examining images of these luminous quasars to
determine which type of galaxies they preferred to reside in when we
started to see cases with two optical sources in their centers where we
only expected one.”
After a slight modification of their automated analysis tools, the team
identified 421 promising cases. However, there was still the chance that
many of these were not bona-fide dual quasars but rather chance
projections such as due to stars in our own galaxy. Confirmation
required detailed analysis of the light from the candidates to search
for definitive signs of two distinct quasars. Using the Keck-I and
Gemini-North telescopes near the summit of Maunakea in Hawai’i,
Silverman and his team identified three dual quasars, two previously
unknown: each object in the pair showed the signature of gas moving at
thousands of kilometers per second under the influence of a supermassive
black hole. The Figure shows a newly-discovered dual quasar. The mass
of each black hole is around 100 million times the mass of our Sun. The
companion is redder than its partner, perhaps indicating that it is
partially hidden behind other material left over from the collision
between the host galaxi-es.
Based on these observations, the team estimates that 0.3% of all quasars have two supermassive black holes in the process of merging. The low fraction exemplifies their rarity and the reason so few were found in past searches. However, Shenli Tang, a graduate student at the University of Tokyo and a project member, points out, “In spite of their rarity, they represent an important stage in the evolution of galaxies, where the central giant is awakened, gaining mass, and potentially impact-ing the growth of its host galaxy.” These results demonstrate the promise of wide-area imaging to detect dual quasars for the study of the growth of galaxies and their supermassive black holes. These three detections are just the beginning of results to come with Subaru’s HSC, as the team obtains spectra of many more dual quasar candidates.
Source: Kavli Institute for the Physics and Mathematics of the Universe (IPMU)
Paper details
Journal: The Astrophysical Journal
Title: Dual Supermassive Black Holes at Close Separation Revealed by the Hyper Suprime-Cam Subaru Strategic Program
Authors: John D. Silverman (1,2), Shenli Tang (1,3),
Khee-Gan Lee (1), Tilman Hart-wig (1,3), Andy Goulding (4), Michael A.
Strauss (4), Malte Schramm (5), Xuheng Ding (6), Rogemar Riffel (7,8),
Seiji Fujimoto (9,10), Chiaki Hikage (1), Masatoshi Imanishi (5),
Kazushi Iwasawa (11), Knud Jahnke (12), Issha Kayo (13), Nobunari
Kashikawa (2), Toshihiro Kawaguchi (14), Kotaro Kohno (2), Wentao Luo
(1), Yoshiki Matsuoka (15), Yuichi Matsuda (5), Tohru Nagao (15),
Masamune Oguri (3), Yoshiaki Ono (16), Masafu-sa Onoue (12), Masami
Ouchi (5,16), Kazuhiro Shimasaku (2), Hyewon Suh (17), Nao Suzuki (1),
Yoshiaki Taniguchi (18), Yoshiki Toba (19), Yoshihiro Ueda (19), Naoki
Ya-suda (1)
Author affiliations:
1. Kavli Institute for the Physics and Mathematics of the Uni-verse, The
University of Tokyo, Kashiwa, 277-8583 (Kavli IPMU, WPI) Japan
2. Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hon-go, Bunkyo, Tokyo 113-0033, Japan
3. Institute for Physics of Intelligence, School of Science, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
4. Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Prince-ton, NJ 08544, USA
5. National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
6. Department of Physics and Astronomy, University of California, Los Angeles, CA, 90095-1547, USA
7. Department of Physics & Astronomy, Johns Hopkins University,
Bloomberg Center, 3400 N. Charles St, Baltimore, MD 21218, USA
8. Universidade Federal de Santa Maria, CCNE, Departamento de Física, 97105-900, Santa Maria, RS, Brazil
9. Cosmic Dawn Center (DAWN), Denmark
10. Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, DK-2100, Copenha-gen, Denmark
11. ICREA and Institut de Ciències del Cosmos, Universitat de Barcelona, IEEC-UB, Martí i Franquès, 1, E-08028 Barcelona, Spain.
12. Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidel- berg, Germa-ny
13. Department of Liberal Arts, Tokyo University of Technology, Ota-ku, Tokyo 144-8650, Japan
14. Department of Economics, Management and Information Science,
Onomichi City University, Hisayamada 1600-2, Onomichi, Hiroshima 722-
8506, Japan
15. Research Center for Space and Cosmic Evolution, Ehime University, 2- 5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan
16. Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582, Japan
17. Subaru Telescope, National Astronomical Observatory of Japan (NAOJ),
National Institutes of Natural Sciences (NINS), 650 North A’ohoku
place, Hilo, HI 96720, USA
18. The Open University of Japan, 2-11 Wakaba, Mihama-ku, Chiba 261- 8586, Japan
19. Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake- cho, Sakyo-ku, Kyoto 606-8502, Japan
DOI: https://doi.org/10.3847/1538-4357/aba4a3 (Published August 26, 2020)
Paper abstract (Astrophysical Journal)
Preprint (arXiv.org)
Research contact:
John David Silverman
Associate Professor
Kavli Institute for the Physics and Mathematics of the Universe
The University of Tokyo
E-mail: john.silverman@ipmu.jp
TEL: 04-7136-6550
Media contact:
John Amari
Press officer
Kavli Institute for the Physics and Mathematics of the Universe
The University of Tokyo
E-mail: press@pmu.jp
TEL: 080-4056-2767
Related links
Rare encounters between cosmic heavyweights (National Astronomical Observatory of Japan)
Rare Encounters Between Cosmic Heavyweights (W. M. Keck Observatory)
