Maarten Schmidt’s seminal 1963 paper in Nature, 3C 273: A Star-like Object with Large Red-shift, ultimately led to an “outburst of theoretical work on black holes and observational attempts to detect them,” as noted by Stephen Hawking (in his book, The Universe in a Nutshell). Since the luminosity of quasars is so incredibly powerful and concentrated within a relatively small region of space, it seemed that black holes were the only possible explanations for such energy. It is now accepted that larger quasars are bi-products of supermassive black holes (SMBH’s) – many millions of star masses worth – which gobble and superheat enormous amounts of matter to indulge their insatiable gravitational hunger.
Quasars can emit as much energy per second as a thousand or more galaxies, making them the most intense X-ray and visible light sources known to science. The superheated matter forms in an accretion disc and is slowly devoured by the black hole. If the conditions are right within the immediate environment, collimated streams of magnetized plasma (‘relativistic jets’) can shoot out over a million light years into space, at velocities close to the speed of light. Hayashida et al. (2012) clarify that these jets originate from the “conversion of the gravitational energy of matter flowing onto the black hole to the kinetic energy of the relativistic outflow or tapping the rotation energy of a spinning black hole.”
A Quasar is the ‘Achilles of the Cosmos.’ Its monster black hole quickly swallows surrounding matter into oblivion, ensuring a relatively short but glorious existence. Their photons are their legacy. As Carl Sagan once explained, “when we observe distant quasars 5 billion light years away, we are seeing them as they were 5 billion years ago, before the Earth was formed. (They are, almost certainly, very different today)”. He had previously speculated, the farthest quasars may be 10 or 12 billion light years away. In fact, as we now know, the most distant quasar, ULAS J1120+0641, is almost 13 billion light years from Earth (redshift z = 7.085). These multi-billion year-old quasar photons originate from a time less than a billion years after the Big Bang.
True to their enigmatic background, quasars still inspire intense scientific investigation. They hold the key to better understandings of the early universe. This drives researchers to develop ever more precise observational technologies, designed to advance the debate surrounding quasar-induced galactic development; examine physics under extreme (‘relativistic’) conditions; and to one day directly observe the immediate environment of a black hole (a long held objective of astrophysics). In 2012, the latter of these goals advanced markedly.
On July 18, an international team of astronomers announced that research data, gathered by an intercontinental network of submillimetre wavelength radio telescopes, allowed them to observe a quasar five billion light years from earth – with a clarity two million times that of human vision.
The observation of quasar 3C 279 was the sharpest direct observation of the centre of a distant galaxy ever made. This observation holds substantial implications for the future of supermassive black hole imaging. Quasar 3C 279 draws its energy from a supermassive black hole one billion times more massive than the Sun, and the accuracy of this latest observation (to within 0.5 light years of 3C 279’s nucleus) is considered “quite remarkable” by scientists from the Max Planck Institute for Radio Astronomy, who led the historic research effort (in association with the Onsala Space Observatory and the European Southern Observatory).
Very Long Baseline Interferometry (VBL) was used to link three telescopes for joint observation: The Atacama Pathfinder Experiment Telescope (Chile), the Submillimetre Array (Hawaii), and the Submillimetre Telescope (Arizona). These three instruments had never been connected in such a way before. Observations were made in radio waves with a wavelength of 1.3 millimetres. As noted by the astronomers, this is “the first time observations at a wavelength as short as this have been made using such long baselines.” With VBL, the longer the “baseline” (i.e. the distance between each telescope), the sharper the observation – akin to casting the proverbial “wide net.” The baselines for the observation of quasar 3C 279 on 7 May 2012 were: 9447 km (Chile to Hawaii), 7174 km (Chile to Arizona), 4627 km (Arizona to Hawaii). The resulting angular resolution was of 28 microarcseconds – or, 20/20 vision, times two million.
Within the next decade or so, astronomers aim to utilise an extensive arrayof radio telescopes, up to fifty, to create what is known collectively as the “Event Horizon Telescope” – a long-term international collaborative project between numerous teams of radio astronomers. The results promised by the Event Horizon Telescope have been a long time coming for observational astronomers, with the prospects for significant advances in knowledge now tantalisingly close at hand. “It would be an amazing thing,” says Daniel Marrone, of the University of Arizona’s Steward Observatory, “it’s never been done before, getting an image of a black hole.” MIT’sHaystack Observatory says, “A long standing goal in astrophysics is to directly observe the immediate environment of a putative black hole with angular resolution comparable to the event horizon. Realizing this goal would open a new window on the study of General Relativity in the strong field regime, accretion and outflow processes at the edge of a black hole, the existence of an event horizon, and fundamental black hole physics.”
Quasars offer the chance for researchers to examine physics under some of the most extreme possible conditions, including the prolific acceleration of particles and production of high energy photons; relativistic gas dynamics, turbulence and plasma processes; the observational effects and illusions brought about by such processes; and potentially exotic forms of matter. Things also get interesting beyond the immediate environment of the feeding frenzy. Astronomers are accumulating a significant body of evidence that suggests quasars played a vital role in the formation of galaxies in the early universe. As noted previously, plasma jets of immense power and reach are a consequence of supermassive black holes. But what is the extent of the influence of these jets on the surrounding intergalactic medium (IGM)? As outlined in Ilana Joanne Klamer’s 2006 PhD thesis, this is an important area of astrophysics that merits further investigation:
“The highly relativistic, supersonic jets that power into the surrounding medium and slam into the existing overdensities can trigger star formation along cocoons surrounding the jets or could modify the stellar initial mass function as a result of the effect of enhanced cosmic ray ionisation in the molecular cores. Therefore, it will also be along these same preferential directions that the first heavy elements — including carbon and oxygen — will be produced as the stars end their lives and enrich their surroundings”.
“There is little doubt that relativistic plasma jets from radio galaxies and quasars deposit appreciable amounts of energy into their surrounding IGM. However, debate continues to rage over the jets’ specific influence. Determining the true extent of this influence is an interesting and important question in astrophysics: the ability to trigger large scale star formation in the early universe could finally explain the ‘rapid enrichment’ conundrum in high-redshift radio galaxies and quasars whereby chemical enrichment of the IGM around these sources has taken place on timescales much shorter than predicted by traditional star formation scenarios”.
In 2009, Elbaz et al. drew attention to “converging evidence that radio jets may trigger galaxy formation”, whilst highlighting the importance of increasing equipment sensitivity for future observations. More recent evidence published in 2012 by Borguet et al. reveals that energetic quasar outflow – as observed in quasar SDSS J1106+1939 – can indeed reach the necessary power to significantly influence the AGN and therefore galactic formation.
According to the research team, “This is the first time that a quasar outflow has been measured to have the sort of very high energies that are predicted by theory… “We couldn’t have got the high-quality data to make this discovery without the VLT’s X-shooter spectrograph. We were able to explore the region around the quasar in great detail for the first time.” This is yet another example of quasar research driving developments in radio astronomy technology. In fact, the Very Large Array (VLA) in New Mexico, one of the world's premier astronomical radio observatories, was built to observe quasars with optical resolution.
Whilst radio astronomy has generated an incredible wealth of high angular resolution data on galactic nuclei, quasars and pulsars over the past few decades, numerous challenges will need to be overcome in order for radio astronomy to remain on the forefront of discovery over the next few decades. Ekers & Bell (2000) cite unprecedented international cooperation and joint mega project funding as fundamental realities for future projects – along with the need to ensure extensibility of past and present technologies, overcoming orbital and terrestrial interference, plus dealing with issues of funding and government policy.
To address the inherent limitations of Earth-based observation and orbital interference, more radical, long-term solutions are being developed. For example, the Lunar Radio Array (LRA) project aims to make surface-based radio telescope observations from the far side of the Moon, focusing on the highly redshifted line of the spectrum. The ultimate mission goal: Nothing short of conquering one of the last frontiers of Cosmology – the Dark Ages – the edge of Genesis, when the first stars were being formed.
As Ekers & Bell noted, the entire radio spectrum is needed for redshifted lines; and according to the LRA team, “The far side of the Moon is likely the only site in the inner solar system for exploiting this potential fully as significant obstacles exist to ground-based telescopes, including heavy use of the relevant portion of the spectrum by both civil and military transmitters and distortions introduced by the Earth's ionosphere.” The LRA would also answer fundamental questions about the formation and influence of the first black holes, and obviously, quasars.
The potential offered by the observational purity of space has been described as “limitless.” For this reason, the future of observational astronomy will edge inevitability closer to the stars. However, it will always be remembered that those perplexing objects of impossible brilliance, the quasars, lit the way.