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.
The abstract mathematical concepts of Albert Einstein’s and Karl Schwarzschild’s ‘point masses’, formulated in the early 20th century, were slowly transformed into the astronomical concept of black holes by some of the world’s greatest physicists. Arthur Eddington commented on the fact that these black holes would not emit any light, so would not have a spectrum. Space-time would curve around these objects. Subrahmanyan Chandrasekhar calculated that bodies above a certain mass threshold would collapse to form black holes, and Freeman Dyson and Andrew Lenard proved that atoms could only be compressed to a certain extent, leading to the determination that neutron stars above this Chandrasekhar limit could exist due to the Pauli exclusion principle.
Our understanding of the more detailed properties of black holes was developed during the latter half of the 20th century. In Nature, Stephen Hawking completed his analogy of black hole physics to the laws of thermodynamics. He showed that black holes could emit radiation (later called “Hawking radiation”) in accordance with its surface gravity (Hawking 1974). Working with colleague Gary Gibbons, Hawking found indirect observational evidence for black holes by considering short-period binary systems with eccentricities (Gibbons & Hawking 1971). In a typical short-period binary system any initial eccentricity would be rapidly dissipated by tidal friction or magnetic breaking. However, in a short-period binary containing a black hole, tidal dissipation only acts on the stellar partner, meaning that any eccentricity in the system is long-lived, and thus potentially observable.
Most of the black holes we know of fit into one of two mass regimes: stellar mass black holes, on the order of five to tens of solar masses, and supermassive black holes (SMBHs), on the order of 0.1-1,000 million solar masses. SMBHs exist at the centre of most, if not all, galaxies. Our Galaxy is no exception: Rainer Schödel and collaborators, writing in Nature, showed unequivocally that the Milky Way is host to a SMBH of nearly 4 million solar masses, in the region known as Sagittarius A* (Schödel et al. 2002). Rainer Schödel and his team followed the motion of a star around Sgr A*, finding it on a highly elliptical keplerian orbit. However, in general, should a star pass too close to a SMBH, Martin Rees laid out what would be the fate of that star: total engulfment or tidal disruption (Rees 1988). These tidal disruption events can be extremely energetic, radiating more energy than supernova explosions. Only a dozen or so have been observed to date.
A phenomenon thought to be related to that of black holes is that of the short gamma-ray burst (GRB). One of the first connections between black holes and short GRBs was made in Nature by Neil Gehrels and colleagues (Gehrels et al. 2005). They managed to localise the origin of a short GRB to a luminous elliptical galaxy, exactly where one would expect a black hole–neutron star binary merger to occur, and conversely, where a supernova explosion (the origin of long GRBs) would be very unlikely. The link between short GRBs and stellar-mass black hole mergers was strengthened in 2013 when Nial Tanvir reported observations of a ‘kilonova’ associated with a GRB (Tanvir et al. 2013). A kilonova is a faint transient event resulting from the decay of neutron-rich radioactive species, which results from the merger of two compact objects: neutron stars or a neutron star–black hole pair.
