Nature's Astronomical Highlights
The journal Nature has been at the pinnacle of scientific publishing for many years. Founded by an astronomer, Norman Lockyer, it has had an extensive history in publishing the most significant developments in the Natural Sciences. For instance, James Chadwick published his discovery of the neutron in Nature; James Watson and Francis Crick presented the helical structure of DNA. Naturally, astronomy has been no exception: part of the discussion following the “Great Debate” on the nature of the Spiral Nebulae (were these small nebulae within our Galaxy or distant galaxies in their own right?) was contained in Nature’s pages in the early 1920s. In the 1960s, Maarten Schmidt’s discovery of the first quasar and Antony Hewish & Jocelyn Bell’s discovery of the first pulsar were presented in Nature. Even up until the present day, Nature is publishing discoveries that not only are of great interest to professional and amateur astronomers and astrophysicists, but also of relevance to humankind in general. In 2016 we discovered through the work of Guillem Anglada-Escudé and collaborators that the nearest star to our Solar System harbours a rocky planet in a temperate orbit.
It is on the back of these discoveries and this extensive history that Nature Research is launching a new journal in 2017, Nature Astronomy, so that more astronomical research might be published with a similar high standard of editing, peer review and production as Nature’s. To celebrate Nature’s comprehensive astronomical heritage, we at Nature Astronomy have curated this Web Collection of 40 Nature papers that have had significant impact on astronomical research. Several of these papers have been cited over 1,000 times in the astronomical literature. To include some more recent papers, which have not had the luxury of many years over which to accrue citations, we have also consulted Altmetric scores, which gauge social media impact among other things. The result is a Collection of Letters, Articles and Reviews that have been roughly grouped into seven themes: exoplanets, pulsars, black holes & short gamma-ray bursts, long gamma-ray bursts & supernovae, galaxies, dark matter and the large-scale structure of the Universe. Several of these papers have been selected for Free Access for a limited period; these can be found collected together below, or in the “Free access” tab, above.
Before we delve into these seven topics, there is one stimulating paper that stands apart, written by astronomer and science communicator Carl Sagan and his colleagues (Sagan et al. 1993). It details an experiment performed with the Galileo spacecraft on its way to Jupiter. Galileo was commanded to turn towards the Earth, and capture data with its instruments. Effectively it observed the Earth for signs of life. However, it only just managed to find them: it saw a water-rich atmosphere and surface; it saw signs of biological activity in the high levels of methane; it saw a red-absorbing pigment that might have been responsible for photosynthesis; but the only compelling and indicative detection was that of narrow-band radio emission suggestive of a technological civilisation. The paper presented a unique opportunity to objectively observe our blue marble planet from afar.
Galaxies come in many shapes and sizes, from ellipticals to spirals and dwarfs to giants. They’re actively star-forming and blue, they’re passive and red, or they’re green and in transition between the two groups. One main feature of galaxies that has hit the pages of Nature again and again is the nucleus: the potentially active galactic nucleus that harbours a supermassive black hole. In the early 20th century, these objects puzzled astronomers: they appeared to be like stars, but were bright and had unintelligible spectra. Hence the name “quasar” that began to be adopted: an abbreviation of “quasi-stellar object”. It was Maarten Schmidt who made sense of quasars in the early 1960s (Schmidt 1963), when he found a ‘star’ emitting a thousand times the energy of our entire Galaxy. It clearly was no star, and the familiar shapes of the Balmer lines of hydrogen – but at the wrong wavelengths – led him to realise that the spectrum was redshifted. At a redshift of ~0.16, the ‘star’ must have been distant, and its brightness meant that it was incredibly energetic; the simplest explanation was that he had observed the nucleus of a galaxy.
It wasn’t until the 1980s that astronomers began to fully understand what processes were occurring in galactic nuclei in order to liberate so much energy. Martin Rees and colleagues (Rees et al. 1982) put together an explanation for the quasar: “a spinning black hole surrounded by a torus of gas too hot and tenuous to radiate efficiently”. Magnetic fields anchored in the torus get twisted together and launch jets of relativistic particles that emit radio waves. In this way, gas – a scarce fuel in galactic nuclei – is not needed to “feed the monster”, as Rees put it. This burgeoning field of “active” galactic nuclei (AGN), and particularly the fuelling of AGN, was summarised in Nature at the end of that decade by Isaac Shlosman, Mitchell C. Begelman and Julian Frank (Shlosman et al. 1990).
Some 15 years later, Tiziana Di Matteo, Volker Springel and Lars Hernquist (Di Matteo et al. 2005) performed simulations that explained one of the reasons for the shut-down of the quasar phase of galaxies. They found that following a merger between galaxies, supermassive black holes are fed so much that accretion onto the black hole initially intensifies. However, after a period, the energy expelled by the black hole heats and clears out gas from the nucleus, quenching star formation and limiting black hole growth. In this way, black hole size is self-regulating.
In a cosmological context, the high luminosity of quasars makes them excellent probes of large distances (and therefore high redshifts and early ages of the Universe). Daniel Mortlock and collaborators reported the detection, in Nature, of a quasar at z=7.085 (Mortlock et al. 2011). Not only was this exceptional because it gives us information on galaxies in the Universe just 770 million years after its origin, but also because it probes the epoch of reionisation, when neutral hydrogen started to become ionised. At the time of its measurement, this spectrum of a quasar was the highest quality information from a source at that distance.
The Hubble Deep Field (HDF) is one of the most iconic images in astronomy, revealing reasonably low redshift galaxies (mostly z < 1.5) in optical and UV light. This redshift regime seemingly probed the peak of star formation and metal production in the local Universe. An article in Nature in 1998 (Hughes et al. 1998) presented an image of the galaxies behind those in the HDF, lying in the redshift range 2 < z < 4. The image, taken with SCUBA, a new submillimetre bolometer, was a great complement to the optical/UV image because it confirmed the epoch of peak star formation: it quantified the absorbing effects of dust in distant galaxies, and it revealed galaxies that went undetected in the Hubble Space Telescope image because of their obscuration. It filled out the history of the Universe up to ~12 billion years ago.
Finally, not just galaxies in the distant Universe have featured in the pages of Nature. A recent Letter by Rodrigo Ibata and colleagues (Ibata et al. 2013) looked at the Andromeda galaxy, finding that this spiral galaxy is surrounded by a vast, extremely thin disc composed of co-rotating satellite dwarf galaxies. Such a planar distribution of galaxies causes difficulties for cosmological simulations because it indicates that dwarf galaxies – by far the most common galaxy type – should not be considered to have evolved in collision-less dynamical isolation.
