Ever wondered what feeds the supermassive black hole at the center of our galaxy?

According to a recent high-powered simulation developed by Northwestern University, the spiral arms of galaxies are responsible for scooping up gases to feed their central massive black holes. The spiral arms use gravitational force to gather gases that would otherwise keep orbiting the galaxy center forever. This mechanism enables the gases to fall into a black hole instead.

This also explains the mysterious nature of magnificently radiant, fast-growing black holes called quasars. The gases that fall into these black holes, get heated up. This generates an enormous amount of light. Quasars often outshine their galaxies.

The simulation developed by Northwestern University is the first single computer simulation capable enough to comprehensively account for the numerous forces and factors that play into the evolution of supermassive black holes.

~ Sanchi Wankhade

Researchers used data from the Cassini mission to study the movements of Saturn’s Rings. While some of the movements could be explained by the gravitational pull of Saturn’s moons, others have been attributed to the planet’s core - which appears to be an indistinct mix of ice and rock, called a diffuse core. The planet’s rings were treated as a seismograph to measure the oscillations inside it. Using this technique, they were able to determine the nature of Saturn’s core.

~ Kashika Singh

By combining radio signals from about 70,000 small antennas, which are a part of the Low-Frequency Array (LoFAr), astronomers have captured detailed and high-resolution images of radio waves emitted by galaxies. Radio waves are often used to probe far away galaxies because they don’t get scattered off by interstellar dust or gas. Astronomers believe that these images will transform the field of galaxy evolution and black hole dynamics, and give insights into the role of black holes in star and planet formation.

~ Soumil Kelkar

Space travel fancies us all. Imagining life in zero gravity seems thrilling as well as fun. But at the same time, the altered gravity can adversely affect our physiology. Gravity is the silent but key influencer on the physiological processes of living things. Studies have shown that weightlessness makes watering plants difficult, causing waterlogging and stunted growth. In humans, too, microgravity can cause bodily fluids to shift toward the head, decreasing circulating blood volume and cardiac atrophy, among other complications.

~ Apurva Bhagat

Scientists have spotted a previously unrecognized “break” – a contingent of young stars and star-forming gas clouds, stretching some 3,000 light-years across, in one of the Milky Way’s spiral arms.

The study focussing on the nearby Sagittarius Arm, used data from the now-retired Spitzer Space Telescope and ESA’s Gaia Mission, revealing this structure, moving at nearly the same velocity and in the same direction through space as the arm itself.

The pitch angle of this structure is about 60 - a huge deviation compared to the pitch angle of the arm, which is 12. The pitch angle speaks about the boundedness of a spiral galaxy.

These structures called “spurs” or “feathers” are commonly found jutting off in the arms of other spiral galaxies, and this might be one of the first such structures observed by us in the Milky Way.

~ Giridharan S

Roughly 98% of stars in the Universe would end up as White dwarfs, including the Sun. White dwarfs are core remnants of low-mass stars that have concluded their thermonuclear activity. They are dense, slowly cooling stars that cast off their outer shells of hydrogen and helium and eventually turn into a black dwarf. The prevalent view, however, has been challenged by NASA/ESA Hubble telescope.

Astronomers have found first observational evidence that white dwarfs can still undergo stable thermonuclear activity by burning up the hydrogen in their outer shell. To investigate the physics underpinning white dwarf evolution, Dr. Chen and colleagues compared cooling white dwarfs in Messier-3 and Messier-13, as the two massive globular clusters share the same age and metallicity. However, it was found that Messier-3 white dwarfs are simply cooling stellar cores. Whereas, Messier-13 contains two populations of white dwarfs:-

1) 30%: standard white dwarfs

2) 70%: those which have managed to hold on to an outer envelope of hydrogen, allowing them to burn for longer and hence cool more slowly.

This makes Messier-3 and Messier-13 together a 'perfect natural laboratory'.

The relatively straightforward relationship between age and temperature has led astronomers to use the white dwarf cooling rate as a natural clock to determine the ages of star clusters, particularly globular and open clusters. However, white dwarfs burning hydrogen could cause these age estimates to be inaccurate by as much as 1 billion years.

Our Sun however won’t be a slow-burning white dwarf after 4 billion years. Slow-burning white dwarfs are essentially generated by low-mass, low-metallicity progenitor stars. The research team is now investigating other clusters similar to Messier 13 to further constrain the conditions which drive stars to maintain the thin hydrogen envelope which allows them to age slowly. The discovery challenges the definition of white dwarfs as we consider a new perspective on the way in which stars age.

~ Sanchi Wankhade

Kevin Heng, a theoretical astrophysicist at the University of Bern, Switzerland, has solved the mathematical problem of calculating the light reflections from planets and moons. The change in sunlight reflections from a moon or planet is called a ‘phase curve’, and these phase curves have essential information about the surfaces and atmospheres of the celestial bodies.

Through several telescopes, phase curve measurements have been made, and these had to be compared with the theory which involved complicated mathematics related to radiation physics. Previous attempts to calculate phase curves were made as early as the 18th century by Johann H. Lambert, followed by significant contributions from Henry N. Russell in 1916, Bruce Hapke in 1981 (based on the work of S. Chandrasekhar), and by Viktor Sobolev in 1975. Now, Kevin Heng has developed a new mathematical family of solutions to calculate phase curves and reflection strength (albedo).

These solutions matched well with the computer calculations. Applications of this new theory to analyze phase curves obtained by Cassini spacecraft for Jupiter were successful and agreed with a recent parallel study on the same topic. Currently, Heng is collaborating with Pierre-Auclair-Desroutour (mathematician from Paris Observatory) for further generalization of solutions.

In a Nature Astronomy paper, Keng and his co-authors applied the theory to the data of planet Kepler-7b obtained from the Kepler telescope. They are currently analyzing the TESS space telescope’s phase curve data, and Keng also envisions the application of their work to phase curves obtained by the forthcoming James Webb Space Telescope.

~ Jharnesh Verma

Out of the nearly 5000 exoplanets known today, the vast majority have sizes between 1 to 4 times the radius of Earth. With no analogs in the Solar System, these planets are classified as Super-Earths or mini-Neptunes (typically radius is 1.6 to 2 times the radius of the earth). Mini-Neptunes are water worlds with hydrogen-rich atmospheres.

It has been shown that temperate mini-Neptunes with the right properties can provide habitable conditions in their interiors. Such planets with large oceans and hydrogen-rich atmospheres providing habitable conditions are referred to as Hycean worlds. Hycean worlds are promising candidates for finding extra-terrestrial life as they have expanded the discovery space (possible range of conditions) of potentially habitable exoplanets.

Hycean planets span a wider range of radii and masses relative to habitable planets considered before. They also allow for a substantially wider Habitable Zone (HZ) as compared to the terrestrial HZ motivated by Earth-like conditions. In addition to the dominant gases like hydrogen, helium, water vapour, Hycean atmospheres are expected to have trace quantities of terrestrial biomarkers like DMS (dimethylsulphide), OCS (carbonyl sulphide), nitrous oxide, etc. These biomarkers can be detected precisely in the future, using the James Webb Space Telescope.

~ Soumil Kelkar

Water in any form is a close resemblance to life. Even the slightest possibility of its presence in space amazes us all.

Chandrayaan-2, the second lunar exploration mission developed by the Indian Space Research Organisation (ISRO), was launched in 2019. Even after its crash-landing on the lunar surface, the Chandrayaan-2 is delivering critical observations about the Moon. One of the eight payloads onboard the orbiter has confirmed the presence of water ice in the permanently shadowed regions of the Moon.

The permanently shadowed regions of the Moon are lurking in the craters of the lunar south pole that do not receive any sunlight throughout the year. These areas have not seen a single ray of sunlight in over two billion years. According to NASA, "They appear dark because, unlike on the Earth, the axis of the Moon is nearly perpendicular to the direction of the Sun's light".

Chandrayaan-2 pointed to the distribution of most possible locations for water-ice mixed with lunar regolith within the permanently shadowed regions of Peary crater in the Lunar North Pole. Unlike continuous ice sheets, patchy dirty ice includes ice crystals mixed with regolith from the Moon's surface. Spectral measurements detected the presence of water and hydroxyl, along with several other volatile species, including carbon dioxide, light hydrocarbons, ammonia, and sulfur-bearing species.

~ Apurva Bhagat

Zodiacal Light is a phenomenon in which a roughly triangular white glow is visible on the Zodiac during the night. Due to this, it’s also called False Dawn. It is caused by the scattering of light by the particles of interplanetary dust, approximately 10-300 micrometers in size, orbiting in the solar system.

This dust was earlier hypothesized to have originated from the Asteroid Belt or comets. But, data from the Juno Mission largely disproved this. Collisions between the particles from the dust and the large solar panels on the probe gave this data. When the probe was inside the dust cloud responsible for Zodiacal Light, the number of collisions peaked around the martian orbit and decreased steadily, stopping almost entirely near the Asteroid Belt. This was a direct contradiction.

Considering that most of the collisions happened between the area between the orbits of the Earth and Mars, Mars might be responsible for the dust clouds that are the cause of Zodiacal Light. Mars has frequent dust storms, during which it might throw off a considerable amount of dust.

Additionally, both Mars and the Zodiacal Light follow a circular orbit while asteroids have an elliptical orbit. Though, why this dust becomes interplanetary dust is unclear, as Mars should have enough gravitational energy to pull back most of this dust.

~ Kashika Singh

In the twelfth century, astronomers spotted a new star in the sky that was visible for around six months. The origin of the supernova SN1181 has remained a mystery for nine centuries, but recently astronomers have announced that they might have found a promising candidate.

According to a new study published in The Astrophysical Journal, the Pa30 nebula has the right age, location, and profile to be the remnant of the SN1181 supernova. The paper, written by an international team of astrophysicists, found that the Pa30 nebula is expanding at the mind-boggling speed of 1100 kilometers per second. Using this speed, they were able to deduce that the nebula was created around the same time SN1181 appeared over medieval skies.

Previous research indicates that the Pa30 nebula and the star (Parker’s Star) contained within was the result of a merge of two white dwarf stars. If this is true, then SN1181 could have been a Type 1a supernova. These supernovae are relatively fainter but fade slowly. This is corroborated by the descriptions recorded by astronomers nearly a millennium ago.

According to one of the authors of the paper, this discovery is significant because “it is the only such event where we can study both the remnant nebula and the merged star, and also have a description of the explosion itself.” Follow-on research might be able to further our understanding of the still poorly understood Type 1a supernovae.

~ Srirang Nabar

Analysis of data from the VLA (Very Large Array) Sky Survey has confirmed the first-ever observation of a brand-new kind of supernova, never before observed, but predicted.

Supernovae usually occur when massive stars explode due to a shortage of nuclear fuel. In this case, however, the explosion was premature and was merger-triggered – meaning, a compact companion object triggered the explosion of its companion star.

Hallinan and his team searched for radio transients, which are short-lived sources of radio waves. It is an excellent way to identify unusual astronomical events, like explosions of massive stars, and neutron star mergers.

Named VT 1210 + 4956, an extremely luminous source of radio waves from the VLA survey’s data set was observed. Dillon Dong – who identified this anomaly - determined this source to be a star with a dense and thick shell of gas. He predicted that a gas shell was cast off the star about a few hundred years ago, then when the star finally exploded into a supernova, that might have interacted with the cast-off gas shell. But, the timescale of the casting off of the gas shell, and the gas shell itself, were unusual.

Anna Ho, a graduate student, suggested the comparison of this radio transient with a catalogue of brief X-ray events. Some of these X-ray events were only a few seconds long. A source of X – rays matched with the position of VT 1210 + 4956. Careful analysis showed that the X – rays and the radio waves were most likely coming from the same event.

Dong explained that the X-ray transient was unusual, and it showed that a relativistic jet of material was launched during the time of the explosion. The material from the resultant explosion later crashed into a massive torus of dense gas that was ejected from the star centuries earlier.

Careful modeling of the phenomenon showed that the remnant of a previously exploded star was orbiting the star in question. This remnant, which could be a black hole or a neutron star, was siphoning away the atmosphere of the star and ejecting it to space, forming a torus of gas. Through this process, the star and this remnant came closer and closer, finally collapsing the system and exploding as a supernova.

X – rays were ejected from the core of the star at the moment of collapse. By contrast, the radio waves came much later, when the exploded material reached the gas torus that was ejected hundreds of years ago.

A massive star and a compact companion object could form a stable orbit, in which they spiral closer and closer over an extremely long period of time forming a binary system. They collide after billions of years, emitting gravitational waves like the ones found by LIGO in 2015 and 2017.

However, in the case of VT 1210 + 4956, the two objects in question collided immediately and catastrophically, sending out blasts of X – rays and radio waves. Though collisions like this were predicted theoretically, this was the first concrete evidence of this happening.

~ Giridharan S