Open Access
South Asia historical documents, how fast the Universe is expanding, fast radio bursts puzzle astronomers, Stars are eating planets, the Diamond Sūtra in Chinese is the worlds oldest printed book
UPDATE: The South Asia Open Archives (SAOA), launched in 2019 by the Center for Research Libraries (CRL), now contains more than one million pages of digitized open-access primary source material. The multidisciplinary materials cover topics ranging from political history through the fine arts to the sciences and represent twenty-seven different languages—Hindi, Bengali, Kannada, Telegu, Gujurati, and Nepali.
One cosmological conundrum is how fast the Universe is expanding, which is measured by a number called the Hubble constant. Two new papers have successfully used a new technique – involving light from an exploding star that arrived at Earth via multiple winding routes through the expanding Universe – to measure the Hubble constant.
Fast radio bursts – intense, milliseconds-long flashes of radio energy from outer space – have puzzled astronomers since they were first spotted in 2007. A single burst can emit as much energy in its brief life as the Sun does in a few days. The great majority of the short-lived pulses originate outside our Milky Way galaxy. We don’t know what produces most of them, or how.
For the first time, astronomers have captured images that show a star consuming one of its planets. The star, named ZTF SLRN-2020, is located in the Milky Way galaxy, in the constellation Aquila. As the star swallowed its planet, the star brightened to 100 times its normal level, allowing a 26-person team of astronomers to detect the event as it happened.
The Diamond Sūtra in Chinese language, complete with a beautifully illustrated frontispiece, is the world's earliest dated, printed book. Produced on the 11 May 868, it was found in a holy site called the Mogao (or ‘Peerless’) Caves or the ‘Caves of a Thousand Buddhas,’ which was a major Buddhist centre from the 4th to 14th centuries. This long cliff wall, carved with 492 caves, is located near Dunhuang, an oasis-town at the junction of the northern and southern Silk Roads, in the present-day province of Gansu (Northwest China).
South Asia Open Archives
The South Asia Open Archives (SAOA), launched in 2019 by the Center for Research Libraries (CRL), now contains more than one million pages of digitized open-access primary source material. More than two dozen institutions have contributed to this ever-growing archive. The multidisciplinary materials cover topics ranging from political history through the fine arts to the sciences and represent twenty-seven different languages—Hindi, Bengali, Kannada, Telegu, Gujurati, and Nepali, just to name a few.
Almost 19,000 pages from the Bangla-language newspaper Yugāntara and the English-Bangla newspaper Amrita Bazar Patrika can be viewed and downloaded. Access to these region-specific papers is supplemented by digitized colonial reports on the “native” newspapers published in the Bombay Presidency; the Madras Presidency; Berar Province (Hyderabad); Punjab, North-Western Provinces, and Oudh; and Bengal. Other English-language colonial records include official reports from the government of Orissa and Bihar; Madras Presidency; and Bombay Presidency. Medical journals, archaeological reports, and census records can also be found in the colonial archive.
Read more here.
The Universe is expanding, but how fast?
One cosmological conundrum is how fast the Universe is expanding, which is measured by a number called the Hubble constant. And there is quite a bit of tension around it. In two new papers led by my colleague Patrick Kelly at the University of Minnesota, we have successfully used a new technique – involving light from an exploding star that arrived at Earth via multiple winding routes through the expanding Universe – to measure the Hubble constant. The papers are published in Science and The Astrophysical Journal.
We have known since the 1920s that the Universe is expanding.
Around 1908, US astronomer Henrietta Leavitt found a way to measure the intrinsic brightness of a kind of star called a Cepheid variable – not how bright they appear from Earth, which depends on distance and other factors, but how bright they really are. Cepheids grow brighter and dimmer in a regular cycle, and Leavitt showed the intrinsic brightness was related to the length of this cycle.
Leavitt’s Law, as it is now called, lets scientists use Cepheids as “standard candles”: objects whose intrinsic brightness is known, and therefore, whose distance can be calculated.
How does this work? Imagine it is night, and you are standing on a long, dark street with only a few light poles going down the road. Now imagine every light pole has the same type of light bulb, with the same power. You’ll notice the distant ones appear fainter than the nearby ones.
We know that light fades proportionately to its distance, in something called the inverse-square law for light. Now, if you can measure how bright each light appears to you, and if you already know how bright it should be, you can then figure out how far away each light pole is.
In 1929, another US astronomer, Edwin Hubble, was able to find a number of these Cepheid stars in other galaxies and measure their distance – and from those distances and other measurements, he could determine that the Universe was expanding.
This standard candle method is a powerful one, allowing us to measure the vast Universe. We are always looking for different candles that can be better measured, and seen at much greater distances.
Some recent efforts to measure the Universe further from Earth, like the SH0ES project I was a part of, led by Nobel laureate Adam Riess, have used Cepheids alongside a type of exploding star called a Type Ia supernova, which can also be used as a standard candle.
There are also other methods to measure Hubble’s constant, such as one that uses the cosmic microwave background – relic light or radiation that began to travel through the Universe shortly after the Big Bang.
The problem is that these two measurements, one nearby using supernovae and Cepheids, and one much farther away using the microwave background, differ by nearly 10%. Astronomers call this difference the Hubble tension, and have been looking for new measurement techniques to resolve it.
Read more here.
Fast radio bursts from space?
Fast radio bursts – intense, milliseconds-long flashes of radio energy from outer space – have puzzled astronomers since they were first spotted in 2007. A single burst can emit as much energy in its brief life as the Sun does in a few days. The great majority of the short-lived pulses originate outside our Milky Way galaxy. We don’t know what produces most of them, or how.
In new research published in Science, we observed a repeating fast radio burst for more than a year and discovered signs it is surrounded by a strong but highly changeable magnetic field. Our results suggest the source of this cosmic explosion may be a binary system made up of a neutron star whirling through winds of dense, magnetised plasma produced by a massive companion star or even a black hole.
The repeating burst known as FRB 20190520B was discovered in 2022 by astronomers at the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China. Repeating fast radio bursts are rare, but FRB 20190520B is the rarest of all: it is the only one that never rests, producing radio bursts a few times an hour, sometimes at multiple radio frequencies. After this intriguing object was first found, astronomers rushed to follow up the initial observation using other radio wavelengths.
Further investigation showed FRB 20190520B resides in an extremely dense environment in a dwarf galaxy 3.9 billion light years away. There are also materials surrounding the FRB source that produce strong, persistent radio emissions. This led to suggestions that the bursting source is a young neutron star in a complex environment. What else can we learn about this intergalactic firecracker and its environment? We carried out observations of FRB 20190520B using CSIRO’s Parkes radio telescope, Murriyang, in New South Wales and the Green Bank Telescope in the United States.
To our surprise, FRB 20190520B turned out to produce strong signals at relatively high radio frequencies. These high-frequency signals turned out to be highly polarised - which means the electromagnetic waves are “waving” much more strongly in one direction than in others. We found the direction of this polarisation changes at different frequencies. Measuring how much it changes tells us about the strength of the magnetic field the signal has travelled through. As it turns out, this polarisation measure suggests the environment around FRB 20190520B is highly magnetised. And what’s more, the strength of the magnetic field appeared to vary over the 16 months we observed the source – and even flipped direction entirely twice.
This change in direction of the magnetic field around a fast radio burst has never been observed before. What does this tell us about FRB 20190520B? Most popular theories to explain recent observations of repeating fast radio bursts involve binary systems made up of a neutron star and either another massive star or a black hole. While we cannot rule out other hypotheses yet, our results favour the massive star scenario.
Massive stars are known to have strong stellar winds with organised magnetic fields around them. If the source of the bursts were moving in and out of the stellar wind region as it travels through its orbit, we would expect the observed magnetic field direction to reverse. The time scale of the magnetic field reversal, the measured variability in the apparent field strength, and the dense plasma surrounding the burst source all fit into this picture.
Our observations might provide crucial evidence to support the hypothesis that sources of repeating fast radio bursts have a massive companion capable of producing highly magnetised plasma. More importantly, the binary hypothesis gives us a prediction for the future. If it is correct, the changes in polarisation of the radio signals from FRB 20190520B should rise and fall over longer periods of time.
So we will be watching. Future observations with Murriyang and the Green Bank Telescope will reveal whether FRB 20190520B is truly in a binary system – or whether the Universe will surprise us once again.
Read more here.
When a star ate a planet
For the first time, astronomers have captured images that show a star consuming one of its planets. The star, named ZTF SLRN-2020, is located in the Milky Way galaxy, in the constellation Aquila. As the star swallowed its planet, the star brightened to 100 times its normal level, allowing the 26-person team of astronomers I worked with to detect this event as it happened.
I am a theoretical astrophysicist, and I developed the computer models that our team uses to interpret the data we collect from telescopes. Although we only see the effects on the star, not the planet directly, our team is confident that the event we witnessed was a star swallowing its planet. Witnessing such an event for the first time has confirmed the long-standing assumption that stars swallow their planets and has illuminated how this fascinating process plays out.
The team I work with searches for the bursts of light and gas that occur when two stars merge into a bigger, single star. To do this, we have been using data from the Zwicky Transient Facility, a telescope located on Palomar Mountain in Southern California. It takes nightly images of broad swaths of the sky, and astronomers can then compare these images to find stars that change in brightness over time, or what are called astronomical transients.
Finding stars that change in brightness isn’t the challenge – it’s sorting out the cause behind any specific change to a star. As my colleague Kishalay De likes to say, “There are plenty of things in the sky that go boom.” The trick to identifying stellar mergers is to combine visible light – like the data collected at Palomar – with infrared data from NASA’s WISE space telescope, which has been surveying the entire sky for the past decade.
In 2020, the star ZTF SLRN-2020 suddenly became 100 times brighter in visible light over just 10 days. It then slowly started to fade back toward its normal brightness. About nine months before, the same object started to emit a lot of infrared light, too. This is exactly what it looks like when two stars merge together, with one critical difference – everything was scaled down. The brightness and total energy of this event were about a thousand times lower than any of the merging stellar pairs astronomers had found to date.
The idea that stars could engulf some of their planets has been a long-standing assumption in astronomy. Astronomers have long known that when stars run out of hydrogen in their cores, they get brighter and begin to increase in size.
Many planets have orbits that are smaller than the eventual size of their parent stars. So, when a star runs out of fuel and starts to expand, the planets nearby are inevitably consumed.
Read more here.
Printed copy of the Diamond Sutra
This copy of the Diamond Sūtra in Chinese language, complete with a beautifully illustrated frontispiece, is the world's earliest dated, printed book. It was produced on the 11 May 868, according to the Western calendar. It was found in a holy site called the Mogao (or ‘Peerless’) Caves or the ‘Caves of a Thousand Buddhas,’ which was a major Buddhist centre from the 4th to 14th centuries. This long cliff wall, carved with 492 caves, is located near Dunhuang, an oasis-town at the junction of the northern and southern Silk Roads, in the present-day province of Gansu (Northwest China).
In 1900, a monk named Wang Yuanlu discovered the sealed entrance to a hidden cave, where tens of thousands of manuscripts, paintings and other artefacts had been deposited and sealed up sometime around the beginning of the 11th century. This copy of the Diamond Sūtra was one of such items and was brought to England by the explorer Sir Aurel Stein in 1907.
The Diamond Sūtra is one of the most influential Mahāyāna scriptures in East Asia. Thanks to the colophon – the short dedication note written at the end, after the sacred Buddhist text – we have quite a lot of information about the context surrounding the commissioning of this particular copy. The few characters translate as follows: ‘On the 15th day of the 4th month of the 9th year of the Xiantong reign period, Wang Jie had this made for universal distribution on behalf of his two parents.’ We therefore know the precise date the scroll was made (11 May 868), who financed it, on behalf of whom and for what purpose.
Each section of the scroll was printed separately, by using a single wood block, and then joined to the others in order to form a 5-metre long horizontal roll. This makes this copy of the Diamond Sūtra not only the earliest surviving dated piece of printing, but also the most substantial one. The intricate frontispiece depicts the historical Buddha addressing his elderly disciple Subhūti, surrounded by an assembly gathered under a grove of trees. The finesse in the details evidences the fact that printing had already grown into a mature technology by the 9th century in China.
The British Library is part of the International Dunhuang Project, a ground-breaking collaboration which aims to make more than 100,000 manuscripts, paintings and artefacts from Silk Road sites available on the internet.
See more of the Diamond Sutra here.
Listen to an audio description of the Diamond Sutra here.