Monthly Archives: March 2022

I think its fair to say the results exceeded everyones expectations.

Between May and June 2018, the MeerKAT radio telescope observed the center of the Milky Way using 64 antennas located in the Karoo region of South Africa. After more than 200 hours of observations and 3 years of data analysis, the South African Radio Astronomy Observatory (SARAO) released spectacular images of the region near the supermassive black hole in the center of our galaxy, 25,000 light-years from Earth.

Ian Heywood, a senior researcher at the University of Oxford who led the team that analyzed the data, explained that the galactic center was chosen to demonstrate the possibilities of MeerKAT because the region is a notoriously difficult part of the sky to image at radio wavelengths, because of the very bright emission and complicated structure. I think its fair to say the results exceeded everyones expectations.

Radio astronomy is still emerging from its infancy. Just 90 years before MeerKAT became operational, radio engineer Karl Jansky built a 30-meter antenna while working for Bell Telephone Laboratories in New Jersey. He had been commissioned to find the cause of static in transatlantic telephone callsand found that the radio interference came from outer space. At the time, astronomers did not pay much attention to his work. For Heywood, the first radio astronomer who made an impact was Grote Reber, who illustrated the possibilities of radio astronomy by mapping cosmic radio sources in the galaxy in 1968.

Leaps and bounds is how Emily Rice, an associate professor at Macaulay Honors College at the City University of New York, described current advancements in radio astronomy. The angular resolution is so amazing, the sensitivity is so amazing, she added, that we can turn [radio frequencies] into actual pictures.

With new and more powerful radio telescopes, however, there is a need for more efficient ways to process the huge volumes of data, as well as better calibration and imaging algorithms. Observations from MeerKAT to the galactic center produced about 2 terabytes (2,000 gigabytes) of data per day, and there are other observations at MeerKAT that produce even more data, said Fernando Camilo, chief scientist of SARAO. (In comparison, the Hubble Space Telescope produces about 140 gigabytes of data per week.)

Necessity is the mother of invention[and] many novel developments in this area are being led by South African scientists, said Heywood. One of these scientists is Isabella Rammala, a Ph.D. student at the Rhodes Centre for Radio Astronomy Techniques and Technologies at Rhodes University in Makhanda, South Africa. Rammala is interested in identifying pulsar candidates in the galactic center imaged by MeerKAT. I spent most of my time on my computer writing code, she explained, processing the images or cleaning the dataremoving things like radio interference and correcting for instrumental effects and sky effects.

Radio astronomy offers several technical and practical benefits to scientists. Its observations are not obscured by interstellar gas or dust, sunlight, or anomalies in Earths own atmosphere. This means that unlike optical telescopes, radio telescopes can be built at sea level and observations can be made both night and day. For Rammala, studying the universe in multiple wavelengths such as radio, infrared, and gamma ray gives us somewhat of a complete picture of what is going on.

Jackie Villadsen is a visiting assistant professor at Vassar College in New York and an astrophysicist who uses radio astronomy to study nearby stars and their interactions with planets. She said observing the universe with different types of wavelengths reveals vastly different pictures. Radio waves are good for studying extremes, high-energy processes, and very large objects.

According to Villadsen, new and more powerful radio telescopes with better imaging capabilities will help [astronomers] see analogues to the Sun and Jupiter in exoplanetary systems. For example, coronal mass ejections (CMEs) are fairly easy to detect with radio astronomy. Flares can strip away an atmosphere and bake a planets surface, and red dwarf stars, many of which likely have small, rocky planets, have a higher flare rate than the Sun. Detecting stellar CMEs with radio telescopes will help astronomers determine whether planets around red dwarfs are habitable or friendly to life as we know it, said Villadsen.

In addition, astronomers hope to detect radio bursts produced by the aurorae of exoplanets, similar to those produced by aurorae on Jupiter. Detecting these radio waves will permit scientists to determine the planets magnetic field strength, which would reveal information about a planets interior structure and how well it can hold on to its atmosphere when its blasted by material from the star. This might even become a method for detecting new exoplanets, added Villadsen.

Right now, its something of a golden age for radio astronomy.

For Rice, theres always going to be technological advancements, but the most important thing is the effects telescopes have in the communities in which theyre located. For example, when MeerKAT made a call for open time observation proposals in 2020, more than a third of the proposals accepted through a dual anonymous review process were from South African researchers.

According to Camilo, around 10% of SARAOs yearly budget goes to scholarships and grants to support human capital and developmentfrom science projects in a high school in a town near the telescope, to Ph.D. fellowships, to more public support for radio astronomy in South Africa.

Right now, its something of a golden age for radio astronomy, added Heywood.

Santiago Flrez (@rflorezsantiago), Science Writer

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With MeerKAT, Astronomers Peer at the Possibilities of Radio Imaging - Eos

An artistic rendition of Oumuamua, which Loeb believes may have been an alien attempt at contact with Earth. Credit: Nagual Design/Wikimedia Commons/CC BY-SA 4.0

Harvard astronomer Dr. Avi Loeb believes that aliens may have tried to contact us in 2017, when an object called Oumuamua flew past Earth.

In a book published in early 2021, Loeb, who was the head of Harvards astronomy department, asserts that the object may have been extraterrestrial in origin.

When the elongated, red-colored object was spotted in space, both scientists and alien enthusiasts took notice. Not shaped like natural space objects like comets and asteroids, Oumuamua was blunt in shape, measuring about a half mile in length.

The name Oumuamua comes from the Hawaiian for scout.

While the majority of scientists who have studied the object believe it is natural in origin, Loeb argues that it wouldnt be wise to rule out the alien hypothesis.

In his book Extraterrestrial: The First Sign of Intelligent Life Beyond Earth, Loeb contends that Oumuamua is unlike any other space object known to man, and may be the product of alien technology.

Loeb stated in an email to Motherboard that The most exciting aspect of the possibility that Oumuamua is weird and unlike any asteroid or comet that we had seen before is that it might be a product of an alien technology.

If so, we might not be the sharpest cookie in the jar or the smartest kid on the block. We should search for additional interstellar objects to find out, he continued.

He rejected the mainstream opinion that, although undoubtedly strange and unique, Oumuamua was likely just a natural space object and not a product of aliens.

Most of the mainstream astronomy community continued with business as usual and ignored Oumuamuas anomaliesSome mainstream astronomers tried to explain the anomalies but needed to invoke objects that were never seen before, like a hydrogen iceberg or a dust bunny, that are not likely to survive the long interstellar journey.

For its part, NASA states that the object likely came from another solar system and did not behave like a comet in space. Astronomers have never seen a natural object with such extreme proportions in the solar system before, according to NASA.

When Oumuamua was first charted in 2017, Loeb argued that the Green Bank Telescope in West Virginia should listen for radio waves coming from the object to help determine if it was an attempt at contact from extraterrestrials, but no radio waves were discovered.

My point is that it is very difficult to explain the weird properties of Oumuamua with conventional natural processes, so studying objects of its type in the future will either educate us about an unusual natural source or about another civilizationLets collect evidence, and not rely on prejudice, he stated.

Loeb is an Israeli-American theoretical physicist and astronomer. He currently serves as the Frank B. Baird Jr. Professor of Science at Harvard, and was the longest serving chair of the Department of Astronomy at the prestigious university.

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Top Harvard Astronomer Believes Aliens Have Tried to Contact Us - Greek Reporter

It's not too often that a new kind of star is seen in the sky, let alone two examples of it. Especially when it comes to dead stars eating other dead star and leaving behind a star that looks like it's still dying but is in fact previously and still dead.

Yeah, let's back up a sec.

A star like the Sun generates energy by fusing hydrogen into helium in its core. Over time the inert helium builds up, and gets heavily compressed and terrifically hot. Eventually the core becomes totally made of helium, and radiates so much energy that the outer layers of the star expand to compensate for the extra heat. The star becomes a red giant.

Gas at the surface of this bloated star feels less gravity holding it on, but a huge amount of energy pushing it upward from below. Because of this the gas starts blowing away from the star, and over time the entire outer part of the star is ejected, exposing the core to space. We call that object a white dwarf. Specifically a helium white dwarf, since it's almost entirely made of helium.

Sometimes, though, there are different steps that happen between the star being a red giant and becoming a white dwarf. For example, if there's enough pressure on the core that the helium can start to fuse too. This makes carbon and oxygen, which usually sink to the center pretty quickly, leaving the helium floating on the surface with just a trace of carbon and oxygen that can be detected. We call these CO white dwarfs, since they're mostly carbon and oxygen, even though we only see small amounts of them on the surface. They can also drive fierce winds of gas away, creating lovely planetary nebulae.

So here's where things start to get weird. There's a kind of star where the core is not a white dwarf quite yet, but is well on its way. The outer layers are mostly blown off and just a thin layer of helium is left, which may still be fusing into carbon and oxygen. These stars have some characteristics that make them look like normal stars what we just call dwarfs, confusingly but they're smaller and fainter, so these are termed subdwarfs. They can be very hot, so they look like what we call O-type normal stars, and these are called sdOs, for subdwarf O stars.

Here's where things recently got even weirder. Astronomers found a pair of unrelated sdOs, both of which had surfaces mostly composed of helium (link to paper). One is called PG1654+322 and is about 9,000 light years away, and the other is PG1528+025 and is 23,000 light years from us.

Now mind you, most hot subdwarfs like these have at most a few percent carbon and oxygen on their surfaces, and even that much is rare. But these two? They have more than just a trace. Way more: While both have surfaces of about 60% helium, they have a whopping 15 and 25% carbon, respectively, and 23 and 17% oxygen.

That's a lot. Like a lot a lot. Where could all that C and O come from?

And here is where the weirdness peaks: They were both probably helium white dwarfs not long ago, and then ate their binary companions. Which were CO dwarfs.

Yeah, I know, what? Let's look at an example of just one pair to avoid more confusion. Basically, things started off long ago with two normal Sun-like stars orbiting each other. Over time, one died, expanding into a red giant, shedding its layers, yadda yadda, and became a CO white dwarf. The other star in the binary did the same thing, but became a helium white dwarf. So now we have two white dwarfs of different types orbiting each other.

Over time they spiraled together, possible by emitting gravitational waves, though the exact mechanism isn't important here. But here's a critical point: The CO dwarf was low mass, and that means it was bigger. White dwarfs are weird that way; they are so unimaginably compressed by gravity that quantum mechanics becomes important, and WM has weird rules. One of them is that matter in these conditions actually shrinks as you add mass, instead of getting bigger. So low-mass white dwarfs are actually larger than high-mass ones.

Why is that important there? Because the surface gravity of the smaller, more massive one the helium one is stronger, and as the two get closer the helium one can strip material off the surface of the other, essentially eating it. Eventually the CO dwarf is gone, consumed by the helium dwarf. The remaining object has a CO white dwarf core mostly covered by helium but will also have a lot more C and O than you'd expect, and looks more like a subdwarf than a white dwarf.

This is a pretty unlikely scenario, as you might expect, because you need pretty exacting conditions to achieve such a weird little object called a CO-sdO in the end. To find one is pretty nifty, but in this case they found two! Which means there are likely more out there waiting to be found.

Why is this important? Stars die in a myriad of ways, and understanding these pathways tells us about how stars live, how they die, and what's left after. Sometimes white dwarfs in binary systems merge and explode, creating extremely powerful supernovae, bright enough to be seen for billions of light years. Sometimes they merge and lack the mass to do this, and we're left with bizarre sdOs that will eventually just become plain old white dwarfs. The vast majority of all stars literally more than 90% will eventually become white dwarfs, so understanding these compact objects is part of understanding stars.

And stars are the building blocks of galaxies, which are the basic components of the Universe itself. And I think that's a pretty good reason to figure all this out. Plus? It's just cool.

Originally posted here:

Bad Astronomy | White dwarfs found that ate their white dwarf companions - Syfy

NASAs Chandra X-ray Observatory has been collecting data on a kilonovaa powerful event illustrated here that happens when two neutron stars mergeassociated with GW170817. This is the first cosmic event that has produced gravitational waves and electromagnetic radiation, or light, that have been detected on Earth. Credit: X-ray data from NASA, CXC and Northwestern Univ./A. Hajela; visual by NASA/CXC/M. Weiss

Astronomers may have detected a sonic boom from a powerful blast known as a kilonova. This eventcalled GW170817is a result of a merger of two neutron stars and is the first object for which both gravitational waves and electromagnetic radiation, or light, have been detected form Earth. Continued detections of this light by NASAs Chandra X-ray Observatoryanalyzed by a collaboration that includes Penn State researchersrevealed this cosmic phenomenon.

Chandra has continued to detect electromagnetic radiation from this neutron star merger nearly four years after the event was first detected, said David Radice, assistant professor of physics and of astronomy and astrophysics at Penn State and a member of the collaboration. These observations provide important information about what happens after the initial collision, such as when and how the two merged objects might form a black hole.

A kilonova occurs when two neutron stars some of the densest objects in the universe merge. On August 17, 2017, astronomers discovered gravitational waves from such a merger using the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) in the United States and the Virgo detector in Italy, coinciding with a burst of gamma rays. Since then, astronomers have been using telescopes all over the world and in space, including NASAs Chandra X-ray Observatory, to study GW170817 across the electromagnetic spectrum, which includes X-rays.

We have entered uncharted territory here in studying the aftermath of a neutron star merger, said Aprajita Hajela of Northwestern University, who led the new study of GW170817.

Astronomers think that after neutron stars merge, the debris generates light in the visible and infrared spectrum from the decay of radioactive elements like platinum and gold formed in the debris from the merger. This burst of light is called a kilonova. In the case of GW170817, visible light and infrared emission were detected several hours after the gravitational waves.

The neutron star merger looked very different in X-rays. Right after the initial LIGO detection was announced, scientists requested that Chandra quickly pivot from its current target to GW170817. At first, they did not see any X-rays from the source, but on Aug. 26, 2017, Chandra looked again and found a point source of X-rays.

This non-detection of X-rays quickly followed by a detection provides evidence for a narrow jet of high-energy particles produced by the neutron star merger. The jet is off-axis that is, not pointing directly towards Earth. Researchers think that Chandra originally viewed the narrow jet from its side, and therefore saw no X-rays immediately after the gravitational waves were detected.

However, as time passed, the material in the jet slowed down and widened as it slammed into surrounding material. This caused the cone of the jet to begin to expand more into Chandras direct line of sight, and X-ray emission was detected.

Since early 2018, the X-ray emission caused by the jet had steadily been getting fainter as the jet further slowed down and expanded. The research team then noticed that from March 2020 until the end of 2020 the decline stopped and the X-ray emission was approximately constant in brightness. This was a significant sign.

The fact that the X-rays stopped fading quickly was our best evidence yet that something in addition to a jet is being detected in X-rays in this source, said co-author Raffaella Margutti of the University of California at Berkeley. A completely different source of X-rays appears to be needed to explain what were seeing.

A leading explanation for this new source of X-rays is that the expanding debris from the merger has generated a shock, like the sonic boom from a supersonic plane. The emission produced by material heated by the shock is called a kilonova afterglow. An alternative explanation is that the X-rays come from material falling toward a black hole that formed after the neutron stars merged. GW170817 would be the first observation of either explanation.

Further study of GW170817 could have far-reaching implications, said co-author Kate Alexander, also from Northwestern University. The detection of a kilonova afterglow would imply that the merger did not immediately produce a black hole. Alternatively, this object may offer astronomers a chance to study how matter falls onto a black hole a few years after its birth.

To distinguish between the two explanations, astronomers will keep monitoring GW170817 in X-rays and radio waves. If it is a kilonova afterglow, the radio emission is expected to get brighter over time and be detected again in the next few months or years. If the explanation involves matter falling onto a newly formed black hole, then the X-ray output should stay steady or decline rapidly, and no radio emission will be detected over time. New Chandra observations of GW170817 from December 2021, which the team is currently analyzing, could help resolve this question.

This observation also paves the way for further study, said co-author Ashley Villar, assistant professor of astronomy and astrophysics at Penn State. When LIGO begins its fourth observing run, we hope to find more kilonovae and really explore the diversity of these events, including how the mass and energy signatures differ in the afterglow and how nonthermal components like jet structure might vary. The richness of this dataset is essential in illuminating the physics driving this diversity.

For more information on this research see:

Reference: The emergence of a new source of X-rays from the binary neutron star merger GW170817 by A. Hajela, R. Margutti, J. S. Bright, K. D. Alexander, B. D. Metzger, V. Nedora, A. Kathirgamaraju, B. Margalit, D. Radice, E. Berger, A. MacFadyen, D. Giannios, R. Chornock, I. Heywood, L. Sironi, O. Gottlieb, D. Coppejans, T. Laskar, Y. Cendes, R. Barniol Duran, T. Eftekhari, W. Fong, A. McDowell, M. Nicholl, X. Xie, J. Zrake, S. Bernuzzi, F. S. Broekgaarden, C. D. Kilpatrick, G. Terreran, V. A. Villar, P. K. Blanchard, S. Gomez, G. Hosseinzadeh, D. J. Matthews and J. C. Rastinejad, 5 April 2021, Astrophysics > High Energy Astrophysical Phenomena.arXiv:2104.02070

A paper describing these results appears in the latest issue of The Astrophysical Journal Letters.

NASAs Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatorys Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

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Astronomers May Have Detected a Sonic Boom From a Powerful Blast Known as a Kilonova - SciTechDaily

It's pretty obvious that the boundary between Earth's mantle and crust has a profound effect on life on the surface: Volcanism and earthquakes are just two events that have a profound and immediate effect.

But new evidence has just been published that the reverse may be true as well. And not only does it appear that life on Earth has an impact on the top of the mantle, that effect can be traced all the way down to the Earth's core.

Whoa.

In the new work [link to paper], scientists looked at kimberlites, igneous rocks created in the mantle that find their way to Earth's surface via violent volcanic eruptions. Kimberlites are the most common source of diamonds, created when carbon deep inside the mantle is squeezed and heated so much it crystallizes.

But not all carbon is created equal. By definition, a carbon atom has six protons in its nucleus, but it can have a different number of neutrons these variations are called isotopes. The most common isotope of carbon has six neutrons, so we call it carbon-12 (or 12C): six protons plus six neutrons. The next most common has seven neutrons, so it's carbon-13 (13C). In general, on Earth, 13C makes up about 1% of all carbon.

The scientists examined 161 kimberlite samples from 69 different places on Earth. These range in age from 12 million to 2 billion years old, and, importantly, they all came from very deep within the Earth. The scientists specifically looked at kimberlites found in areas above deep mantle plumes, which are like conveyor belts of magma that come up from the planet's core/mantle boundary, about 3,000 kilometers beneath the surface.

They found a remarkable pattern: Kimberlites older than about 250 million years all have a higher ratio of 13C to 12C in them than ones that were younger than that age. The difference is small but consistent, and points to some sort of change in the available carbon isotopes in Earth's past that made up the kimberlites. That change is more likely to have occurred on Earth's always-changing surface versus the more stable mantle.

We know that a lot of carbon is recycled by Earth, brought up from the interior and then brought back down by subduction, when a continental plate slides under another and eventually finds itself in the mantle. If carbon from Earth's surface is made into these kimberlites, it takes about 300 million years for it to be dragged down to the core/mantle boundary and then dredged back up. So if something happened to change that carbon isotope ratio on Earth's surface, it happened roughly 550 million years ago.

Which, it so happens, was right around the time of the Cambrian Explosion.

This was a period in Earth's history when life underwent rapid evolutionary diversification, such as the evolution of hard shells that resist erosion and can be found in fossils today, including, famously, trilobites. Life at that time was fruitful and multiplied, raining carbon down into the seabeds, which was then subducted down into the mantle.

Here's the fun bit: Biology tends to prefer 12C over 13C in its chemistry. The extra neutron makes 13C heavier, and it takes more energy to move around and use than its lighter isotopic sister, so life in general uses the lighter 12C isotope (though of course in reality it's more complicated than this).

What this means is that if you look at a lump of inorganic carbon it will have a slightly higher ratio of 13C over 12C than a lump created through biology, because the latter will preferentially keep the 12C around.

What the scientists are positing here is that life got so abundant in the Cambrian Period that it affected the carbon isotope ratio of kimberlites made at the time. That's astonishing.

The logical steps go like this: Life got more abundant on Earth in the Cambrian about 550 million years ago. Life likes 12C, so as organisms died and fell to the seabed they brought a slightly higher mix of that isotope with them. This carbon got dragged down into the mantle, and in some places plunged way down to the Earth's core then back up toward the crust. As it did so it formed kimberlites, and these would have slightly more 12C than average, or, if you prefer, slightly less 13C. Any kimberlites made before the Cambrian Period had more 13C in them, and any made after had less.

Now mind you, there are complications. There are other processes, mostly chemical and geophysical, that can change the 13C/12C ratio, but after looking them over the scientists think that the biological explanation fits the data best.

If they're right, that's pretty dang amazing. Ancient creatures swimming in our prehistoric oceans actually changed the geochemistry of the planet!

or maybe it shouldn't be so surprising. We're changing our planet's chemistry now. We dump 40 billion extra tons of carbon dioxide into our atmosphere every year, outstripping every volcano on Earth combined by a factor of 100. The planet's climate is changing, and in the end it's humans doing that, and we're biology.

I just hope that, 500 million years from now, hyperevolved voles (or whatever) don't find evidence of some previously unknown species that mucked with the planet so much it changed the environment. We've seen it happen before, but hopefully we're smarter than cyanobacteria and trilobites.

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Bad Astronomy | Earth life changed the carbon chemistry of the mantle | SYFY WIRE - Syfy

New Delhi:

Forecasting models are good only for short-term projections and an IIT-Kanpur study predicting a fourth Covid wave in India in June may at best be data astronomy and guesswork, say several scientists.

Dispelling fears of another spike in cases in the next three months, they also took note of the fact that most people in India have had two vaccines and one natural infection. So even if there is a wave, the consequences in terms of hospitalisation and deaths should be manageable unless there is a new variant.

Active cases are decreasing quite fast and from looking at the current trends we certainly cannot say anything about a new wave in the future, said Sithabra Sinha, professor at Chennai's Institute of Mathematical Sciences (IMSc).

The reproductive number (R) the expected number of cases directly generated by one case in a population for India is at the lowest value it has been since COVID-19 broke here in March 2020, he added.

According to the recent modelling study by researchers at the Indian Institute of Technology-Kanpur, the fourth wave of the Covid pandemic in India may start around June 22 and peak from mid- to late-August.

The yet-to-be peer-reviewed study, posted on the preprint repository MedRxiv, used a statistical model to make the prediction, finding that the possible new wave will last for four months.

The research led by Sabara Parshad Rajeshbhai, Subhra Sankar Dhar and Shalabh of IIT Kanpur, also noted that there is always a fair chance that a possible new variant of coronavirus may have an intense impact on the whole analysis.

The study led to animated debate with experts questioning the assumptions made in it.

The precise timing itself is suspect, said Gautam Menon, who has been tracking Covid numbers in India since the beginning of the pandemic. The methodology, in his view, is doubtful and any modelling exercise making predictions months in advance is not trustworthy.

I would not trust any such prediction, especially one with precise dates and times, the professor, Departments of Physics and Biology, Ashoka University in Haryana, told PTI.

We can predict nothing about the future because what new variant may come along is unknown. What we can, however, do, is be vigilant and collect the data that enables us to react fast and effectively, he added.

Public health expert Bhramar Mukherjee agreed, saying the kind of prediction made in the IIT Kanpur paper is akin to data astrology, not data science.

I do not believe in the former. In my experience, forecasting models are very good with short-term prediction two-four weeks ahead of time, Mukherjee, professor of Global Public Health at the University of Michigan, US, told PTI.

Long-range predictions are not reliable. Could anyone predict Omicron during Diwali? We should have some humility of knowledge based on the past, the scientist added.

Theoretical physicist Sinha echoed the views of the others.

I would in any case be fairly sceptical of such long-range predictions.. Given the large number of uncertainties involved, any statement about what's going to happen a few months down the line is no better than just pure guesswork. In epidemiologist Ramanan Laxminarayan's view, there will likely be new, smaller waves of the pandemic but the basis for the IIT Kanpur prediction is not clear.

Emergence of new variants, continuation of vaccination coverage and eventually, a booster policy will determine when and how COVID-19 will re-emerge, Laxminarayan, director of the Center for Disease Dynamics, Economics & Policy in Washington and New Delhi, told PTI.

There are concerns that a future surge may be driven by the highly contagious Omicron BA.2 subavriant, spreading fast in many countries, including in Denmark and the UK, or an entirely new variant that could surprise the world like Omicron did in November last year.

"Already, there is a high level of hybrid immunity present, from a combination of prior infections and vaccinations. The Omicron wave was largely blunted because of this hybrid immunity, but also because that variant was less virulent overall, said Menon.

Laxminarayan added that there is a risk of a future surge. Experience from other countries shows that India's mutant third wave was not because Omicron was much less virulent but because Indians had immunity through prior exposure and vaccination.

We have to watch out for the data, focus on reopening schools and workplaces, keep vaccination efforts going, stock up on antivirals and treatments, and increase mitigation strategies when we see an uptick, just like we did for the Omicron wave, Mukherjee agreed.

Defending their study, authors Rajeshbhai, Sankar Dhar and Shalabh said the scientific calculations used in the paper are based on certain statistical models and scientific assumptions. The usage of such models and assumptions are common in academics and research, they told PTI in a joint email.

We have attempted to make forecasting using some statistical modelling which we think may work in such scenarios. In research, we are always attempting to solve an unknown problem based on scientific framework, the statement said.

But often several assumptions are required for the statistical inferences drawn. However, no one can guarantee the success beyond a certain confidence level, as there can be several factors that could influence the prediction which are mentioned in the preprint of the paper, the authors added.

The authors also noted that any statistical estimation is associated with variability.

We are in the process on addressing the confidence measure of the start and end dates of the fourth wave, that is to say the next wave could start on 22nd June plus-minus a few days, they added.

According to Union Health Ministry figures on Saturday, 5,921 people tested positive for the infection in a day, taking India's case tally to 4,29,57,477 (42.9 million/4.29 crore). Active cases were at 63,878.

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May be data astronomy: Indian experts question study predicting fourth Covid wave in June - DTNEXT