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Early Cosmos around the Quasar
On April 23, 2001, a team of astronomers (including Xiaohui Fan, Robert Becker, Michael Strauss, and Richard L. White) working with the Sloan Digital Sky Survey (SDSS) announced that they had observed a distant "quasar" from the earliest stellar era of the universe (see: news summary; SDSS press release; Becker et al, 2001; and Fan et al, 2001). Light from the object travelled from 13 to 14.5 billion light-years (ly) -- assuming an estimated age for the universe of roughly 14 to 15 or so billion years -- before reaching the Solar System in March 2000, making J1030 the most distant object then detected in visible and x-ray wavelengths (Pentericci et al, 2002; and Malthur et al, 2002). Subsequently, however, an even more distant quasar with a tentative redshift of z=6.40 was announced on January 9, 2003, near the SDSS detection limit of a redshift of z ~ 6.5 for bright quasars, and other teams of astronomers detected even more distant, fast-star-forming irregular proto-galaxies, including: gravitationally-lensed HCM 6A behind galaxy cluster Abell 370 with a redshift of z~6.56, which appears to be converting about 40 Solar-masses into stars annually; (PhysicsWeb; IFA press release; Hu et al, 2002, in pdf; and erratum); and the possible "superwind-galaxy" LAE J1044-0130 (Subaru press release; and Ajiki et al, 2002, in pdf). On June 29, 2011, a team of astronomers using the European Southern Observatory's Very Large Telescope and other telescopes around the world announced their detection of ULAS J1120+0641, which is the oldest known quasar measured thus far with a redshift of z ~ 7.08 and which indicates that its light has taken around 12.9 billion years to reach Earth from just 770 million years after the Big Bang (ESO science release).
Designated by survey catalogue and position as SDSS J103027.10+052455.0 (but often referred to as simply J1030+0524 and hereafter in this text as J1030), this exceptionally luminous quasar was detected despite an extremely high spectroscopic redshift of z = 6.28 +/- 0.03. In addition to two similarly remote quasars found only a week before at redshifts of z = 5.99 and 5.82 on April 16, 2001, J1030 was observed when the universe was only around around seven percent of its present age at around 860 or so million years old (Pentericci et al, 2002). By August 3, 2001, the same team of astronomers announced that they were able to use the quasar to mark the end of the period when radiation from the first stars and quasars tore apart and re-ionized the neutral hydrogen atoms that filled the universe for some 100 million years after the Big Bang (SDSS press release).
Spectra of three remote quasars
show that the Lyman-alpha line
of hydrogen has been shifted
farthest to the right for
SDSS J1030+0524 (more).
According to what has become conventional cosmological theory, the universe after the Big Bang) was composed of a superhot plasma of electrons and quarks that soon formed protons and neutrons. However, the universe took 300,000 years to cool sufficiently for neutral hydrogen and helium gas to form, with traces of lithium and beryllium atoms (at around a redshift of z ~ 1,000). When the first generation of massive stars formed and lit up, the so-called "Cosmic Dark Age" ended. The first stars, however, also began emitting intense ultraviolet radiation that "re-ionized" neutral hydrogen atoms formed after the Big Bang by tearing electrons from their proton nuclei. With lives as brief as three million years, many of these massive stars soon exploded as supernovae and created black holes, of which many soon coalesced into supermassive hole and disk complexes as luminous quasars that emitted their own ionizing radiation. Within a half a billion years or so, not much neutral hydrogen was left around the stars and the quasars at the center of coalescing proto-galaxies. Unlike the two slightly closer quasars that were also found in April 2001, however, the emission absorption impact of neutral hydrogen gas was detected in the spectrum of J1030 dating it to the period when the first stars and quasars formed (Fan et al, 2001; Becker et al, 2001; and Jordi Miralda-Escude, 1997).
In 1965, Jim Gunn (SDSS Project Scientist) and Bruce Peterson predicted that neutral hydrogen atoms would be detected by their light-absorbing signature, creating a trough in the spectrum as hydrogen atoms absorb all the light at a particular, characteristic wavelength. If at least one part in a 100,000 of the hydrogen in intergalactic space were made up of whole atoms, all the light at this wavelength would be blocked. Because light from objects that are distant in space and time is shifted toward the red end of the spectrum, the Gunn-Peterson trough would also be shifted. By looking at where in the spectrum the trough occurred, astronomers could tell how faraway and old those atoms were. Thus, more than 35 years after it was predicted, J1030 was finally found in the early period of the universe where neutral hydrogen gas still existed in quantities sufficient to be detected.
The first stars lit up a few-
"Dark Age" with spectacular
intensity, leading to the
rapid creation of heavy
elements and black holes
that coalesced to form
bright quasars (more).
Astronomical instruments such as the Hubble Space Telescope and the Chandra X-Ray Observatory have uncovered evidence that very first stars may have burst into the universe more intensely and spectacularly than previously theorized. Studies of Hubble's "deep field" views suggest that the universe made a significant portion of its stars in a torrential firestorm of star birth, which abruptly lit up the pitch-dark heavens just a few hundred million years after the Big Bang, the tremendous explosion that created the universe. Though stars continue to be born today in galaxies, the current rate of star birth rate is a trickle compared to the hypothesized baby boom of stars in the early universe.
Larger x-ray & optical collage image.
A lack of bright, remote x-ray sources
in the Hubble Deep Field images
suggests that there was an enormous
amount of star formation in early
proto-galaxies, or that supermassive
black holes were somehow hidden
in the early universe (more).
Analysis of early galaxies in the Hubble deep fields taken near the north and south celestial poles (in 1995 and 1998, respectively) suggest that the farthest objects in the deep fields are only the "tip of the iceberg" of a uniquely effervescent period of star birth. Roughly 90 percent of the light from the early universe appears to be missing in the Hubble deep fields because the previous census of the deep fields missed most of the ultraviolet light in the universe. A new analysis of galaxy colors, however, indicates that the farthest objects in the deep fields must be extremely intense, unexpectedly bright knots of blue-white, hot newborn stars embedded in primordial proto-galaxies that are too faint to be seen even by Hubble's far vision -- as if only the lights on a distant Christmas tree were seen and so one must infer the presence of the whole tree (more discussion at: STScI; and Lanzetta et al, 2002). In 2003, astronomers announced that they had discovered that iron from supernovae of the first stars (possibly from Type Ia supernovae involving white dwarfs) indicate that "massive chemically enriched galaxies formed" within one billion years after the Big Bang, and so the first stars may have preceded the birth of supermassive black holes (more from Astronomy Picture of the Day, ESA, and Freudling et al, 2003).
ESO, ESA, NASA
Type Ia supernovae may have
chemically enriched the first
massive galaxies within one
billion years of the Big Bang
(more from APOD, ESA, and
Freudling et al, 2003).
SDSS observational data show that the number of quasars rose dramatically from a billion years after the Big Bang, but then peaking at around 2.5 billion years later and falling off sharply towards more recent times (SDSS press release). As quasars themselves do not provide enough ionizing photons to keep the universe ionized at z > 5, the major contributor to ionization must have been star-forming galaxies (as happens at z~3: Steidel et al, 2001). Luminous quasars such as J1030 ionized the hydrogen within their vicinity and create an HII region out to several million parsecs -- more than 20 million ly (Pentericci et al, 2002; and Malthur et al, 2002).
Quasar SDSS J1030+0524
The quasar was found in the northeastern corner (10:30:27.1+5:24:55.1, J2000; and 10:30:27.10+5:24:55.0, ICRS 2000.0) of Constellation Sextans, the Sextant. It is located southeast of Rho Leonis and Regulus (Alpha Leonis), northwest of Zavijava (Beta Virginis) and Zaniah (Eta Virginis), and northeast of the Spindle Galaxy (M102 or NGC 5866) and Alphard (Alpha Hydrae). Unfortunately, it has never been visible with the naked eye from the Solar System. A useful catalogue designation for this object is: SDSS J103027.10+052455.0.
Larger image of the accretion disk around the supermassive
black hole in NGC 4261, around 45 million light-years away.
A quasar is seen by the light emitted by gas falling into
a supermassive black hole via its accretion disk, which
astronomers believe is, in turn, surrounded by an even
more massive halo of dark matter (more from CfA,
Science, and Barakana and Loeb, 2003, in pdf).
J1030 appears to have a central black hole of several billion Solar-masses that must have formed within the first billion years of the Big Bang (Brandt et al, 2002). Since the quasar is very old (as much as 13 to 14.5 billion years), astronomers are puzzled that such a supermassive black hole could have formed so soon after the Big Bang (possibly less than a billion years or so). The current explanation is that such quasars and their host galaxies assembled within even larger haloes of dark matter, which enabled them to form very quickly. In January 2003, astronomers (Rennan Barkana and Abraham Loeb) announced their discovery of a shock-wave of ionized gas around J1030 and another early quasar with a supermassive black hole (SDSS J1122-0229 with z=4.75) that could be the fingerprints of dark-matter haloes. As a quasar's black hole sucks in gas from surrounding space, the gas collides with the edge of its dark-matter halo and forms a shock wave, which heats the gas suddenly and strips off electrons to form electrically charged ions. Although the infalling gas absorbs some of the light radiated from the quasar, the gas becomes transparent when it gets ionized. The sudden appearance of transparent gas at the shock boundary breaks up the spectrum of light from the quasar so that it is split into two intensity peaks of different height, instead of rising and falling smoothly as the wavelength changes if was not ionizd. Barkana and Loeb's analysis also suggests that the galaxy surrounding J1030 has around the mass of the Milky Way given the amount of gas falling into its central black hole (CfA press release, Science, and Barakana and Loeb, 2003, in pdf).
SDSS J1030+0524 is believed to be a
supermassive black hole with an accretion
disk of gas and dust and emitting bi-polar
jets of high-energy radiation such as gamma
and x-ray photons (more illustrations).
Metal line ratios indicating greater than Solar abundance were found in the spectrum of J1030 (and of similarly remote quasars). This finding suggests that heavy-element enrichment began quickly in the early universe, soon after the birth of the first stars. Although the Big Bang should have created only hydrogen, helium and trace amounts of lithium and beryllium, J1030's light revealed traces of heavier elements including carbon, nitrogen, oxygen and silicon, which must have been made by stellar processes and supernovae.
Spectra of J1030 and another remote
quasar displayed unexpectedly strong
lines of heavier elements, i.e., carbon,
oxygen, nitrogen, and silicon (more
on the "Gunn-Peterson trough" and
the ionization of neutral hydrogen).
Calculations suggest that J1030 may have been at last 13 to 20 million years old when observed and so the first stars must have formed a few hundred million years prior to the observation of the quasar, possibly at a redshift of z ~ 8.7 when the universe was around 560 million years old (Pentericci et al, 2002; and Haiman and Cen, 2002). The quasar's element ratios are consistent with chemical evolution models suggesting the fast formation of high-mass stars within around half a billion years previously, similar to the nitrogen-rich environment of today's "Giant Elliptical" galaxies (Pentericci et al, 2002).
Quasars are peculiar objects that radiate as much energy per second as a thousand or more galaxies, from a region that has a diameter about one millionth that of the host galaxy. They are intense sources of gamma rays and X-rays as well as visible light. The power of a quasar depends on the mass of its central supermassive black hole and the rate at which it swallows matter. Almost all galaxies, including the Milky Way, are thought to contain supermassive black holes in their centers. Quasars represent extreme cases where large quantities of gas are pouring into the black hole so rapidly that their energy output (from their accretion disk and wind and/or bi-polar jets) are a thousand times greater than the galaxy itself. Because of their relative brightness, high-energy gamma and x-ray quasars have become important probes for astronomers studying distant reaches of the universe and its ancient past. By the turn of the century, over 50 high-energy quasars had been discovered.
As a swirling disk of gas gradually falls into the central
black hole, it heats up and some of the gas is blown off
the disk by intense radiation in a wind at speeds up to
a tenth of light speed (more illustrations).
The three remote quasars discovered in the SDSS images during 2001 looked similar to ones that were less than half as old. Hence, some astronomers believe that the conditions around those central black hole did not appreciatively changed much in that time, contrary to some theoretical expectations. In addition, the masses of the black holes producing the X-rays are huge, given their relative youth. By various estimates, the three quasars had already accumulated between one and 10 billion Solar-masses. By comparison, the Milky Way's central black hole believed to contain less than three million Solar-masses (more discussion).
One team of astronomers analyzed the three distant SDSS quasars with 14 other, somewhat closer quasars that lie between 12 and 12.5 billion ly away. They determined that the younger, more distant SDSS quasars were radiating a lower share of their energy in x-rays. This is consistent with some theoretical predictions that a hot gas atmosphere is associated with the accretion disks swirling around central supermassive black holes, provided that the distant quasars have more massive black holes than nearby ones (Bechtold et al, 2002).
Up-to-date technical summaries on this quasar are available at: NASA's ADS Abstract Service for the Astrophysics Data System; the SIMBAD Astronomical Database mirrored from CDS, which may require an account to access; and the NSF-funded, arXiv.org Physics e-Print archive's search interface.
Constellation Sextans is one of seven (including Canes Venatici, Lacerta, Leo Minor, Lynx, Scutum, and Vulpecula) that were introduced by Johannes Hevelius (1611-1687), whose is known mostly known for his charts of the Earth's Moon. The seven were included in his catalogue of 1564 stars, Prodromus Astronomiae, which was published by his wife three years after his death. In naming this simple constellation, Hevelius commemorated the sextant on which he relied on to view the stars instead of a telescope. For more information about the stars and objects in this constellation, go to Christine Kronberg's Sextans. For an illustration, see David Haworth's Sextans.
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