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Showing posts with label Space & Astrophysics. Show all posts
Showing posts with label Space & Astrophysics. Show all posts

Tuesday, 28 January 2020

A giant star devoured his companion and caused one of the brightest supernovas of all time

When a sufficiently massive star reaches the end of its life, it produces one of the most cataclysmic events in the Universe: a supernova. The light and energy released are such that the event often overshadows all the surrounding objects. However, there is an even more intense phenomenon: hypernovas (or superluminous supernovas). This is what astrophysicists observed in the constellation of Perseus 14 years ago, during the event called SN 2006gy. And recently, they proposed a hypothesis explaining the origin of the phenomenon.

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In September 2006, “a” star 50 billion times brighter than the Sun, and in the process of exploding, located 240 million light years away in the constellation of Perseus, began to shine intensely. For 70 days, the explosion became more and more brilliant, eclipsing its original galaxy by being tens or even hundreds of times more powerful than a typical supernova. At the time, this super bright supernova (also known as a hypernova) was the brightest star explosion ever detected.

What was special about this record explosion (officially named SN 2006gy)? Nobody knew. But now, more than a decade later, astrophysicists may finally have an idea. In a new study published in the journal Science , the researchers re-analyzed the mysterious emission lines emanating from the explosion about a year after its peak.

The SN 2006gy event observed by the Hubble space telescope. Credits: Hubble

A hypernova involving a binary stellar system

The team discovered large amounts of iron in the emissions, which they said could only be the result of the interaction of the supernova with a preexisting layer of stellar material ejected hundreds of years earlier. Where does all this ejected stellar material come from? A likely scenario is that the SN 2006gy event did not start with one star, but with two.

“No one had tried to compare the spectra of neutral iron, that is to say the iron that all the electrons kept, with the unidentified emission lines of SN 2006gy, because iron is normally ionized. We tried it out and saw with enthusiasm how, line after line, the lines were aligned with the observed spectrum,” explains Anders Jerkstrand, of the University of Stockholm.

Many binary systems involve a giant star and a white dwarf. In the SN 2006gy scenario, the white dwarf accelerated matter from the giant companion star while spiraling towards it after being caught in the expansion of its gaseous envelope. Credit: Pearson Ed

"A candidate scenario to explain this is the evolution of a binary progenitor system, in which a white dwarf spirals towards a giant or supergiant companion star" explain the researchers.

Collisions between binary stars (two stars orbiting each other) are rare, occurring once every 10,000 years or so in the Milky Way. When the stars collide, they can eject into the surrounding space a gaseous envelope of stellar material when the two stellar nuclei slowly merge.

The progenitor of SN 2006gy was, according to the new model, a double star composed of a white dwarf the same size as Earth and a massive star rich in hydrogen as large as our Solar System, in close orbit. As the hydrogen-rich star has expanded its envelope, which occurs when nuclear reactions are triggered in the later stages of evolution, the white dwarf has been caught in the envelope and has spiraled towards the center of the companion.

A supernova amplified by the previous collision of the two stars

When it reached the center, the unstable white dwarf exploded and a so-called type Ia supernova was born. This supernova then collided with the ejected envelope, which is projected during the spiral descent of the white dwarf, and this gigantic collision gave birth to the light of SN 2006gy.

Artist's impression showing what the SN 2006gy hypernova could have looked like. Credits: NASA / CXC / M.Weiss

If such a collision had occurred between 10 and 200 years before the supernova was detected, the two stars could have released a gaseous envelope that lingered around the system when the stars merged over the next century. When the fusion finally ended with an explosion of type Ia supernova, the gaseous envelope could have amplified the brightness of the explosion to the staggering levels that astronomers observed, and also produced the appropriate iron emission lines. .

This explanation is, for the moment, purely mathematical, astrophysicists having never seen two binary stars merge. A new clue could come from a nearby star system called Eta Carinae.

Located about 7,500 light years from Earth, Eta Carinae is a pair of giant stars that have exploded slowly over the past few hundred years, gradually lighting up to become the brightest star system in the Milky Way. Researchers believe that stars could end up in hypernova in the next 1000 years.


A type Ia supernova at the heart of superluminous transient SN 2006gy

Anders Jerkstrand, Keiichi Maeda, Koji S. Kawabata

Science  24 Jan 2020

Vol. 367, Issue 6476, pp. 415-418

DOI: 10.1126/science.aaw1469

Thursday, 23 January 2020

ESA launches the first prototype oxygen extraction plant from the lunar regolith

📷 | ESA

NASA's Artemis mission will mark the return of humans to the moon since the last Apollo mission in 1972. But bringing astronauts to lunar soil is not the ultimate goal of space agencies. Some plans aim to install real permanent lunar bases in order to carry out scientific experiments and test different engineering techniques. One of the essential resources to manage to maintain these inhabited bases is oxygen. Even if the Moon does not have an atmosphere, the regolith that lines its surface contains a lot of oxygen. And to test the technique of extracting oxygen from the regolith, ESA will host the first large-scale prototype factory using this process.

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Last year, researchers published an article on how to extract oxygen from a lunar dust simulator (regolith); now the first prototype oxygen plant will attempt this extraction on a larger scale. If it works, the technology could provide humans with important resources that will aid future lunar missions, and perhaps even allow long-term bases and colonies on the Moon.

“ Having our own facility allows us to focus on producing oxygen, measuring it with a mass spectrometer when it is extracted from the regolith simulator. Being able to acquire oxygen from the resources found on the Moon would obviously be extremely useful for future lunar colonists, both for breathing and for the local production of rocket fuel "explains the chemist Beth Lomax of the University of Glasgow , in Scotland.

Oxygen is the main resource necessary for the establishment of permanent manned lunar bases. Geochemists have developed a way to extract the oxygen contained in the regolith. Credits: ESA

Extract the oxygen from the regolith by electrolysis into molten salt

The installation, located at the European Space Research and Technology Center of the European Space Agency in the Netherlands, will use the technique developed by Lomax and his colleagues. Geochemists know, on the basis of samples of the lunar regolith, that oxygen is really very abundant in this material. Between 40 and 45% of the regolith by weight is oxygen.

Using an exact copy of the lunar regolith made on Earth, called a simulator of the lunar regolith, attempts have been made in the past to figure out how to extract oxygen, with poor results - too complicated, too weak, or destructive of the regolith. The Lomax team has remedied this by using a technique called “molten salt electrolysis”.

The electrolysis in molten salt of the regolith extracts oxygen while producing usable metal residues. Credits: Lomax et al., Planetary and Space Science, 2019

First, the regolith is placed in a mesh basket. Calcium chloride - the electrolyte - is added and the mixture is heated to about 950 degrees Celsius, a temperature that does not melt the material. Then an electric current is applied. This extracts oxygen and migrates the salt to an anode, where it can be easily removed. This technique extracts up to 96% of the oxygen from the regolith; as a bonus, the remaining material from this process is a mixture of metal alloys.

Use materials left over from electrolysis

" This is another useful avenue of research, to see what are the most useful alloys that could be produced from these, and for what type of applications could they be used." Could they be 3D printed directly, for example, or would they require refinement? The precise combination of metals will depend on where, on the Moon, the regolith is mined - there would be significant regional differences, "said Alexandre Meurisse of the European Space Agency.

The current configuration of the system is based on commercial deoxidation plants, where oxygen is only a useless by-product which is discharged. However, as the facility evolves, a means of storing oxygen will be included. The end goal, of course, is to develop a system that could work on the Moon, using a real lunar regolith, not a simulator.


ESA opens oxygen plant – making air out of moondust


Friday, 6 December 2019

Microgravity Brings New Hope For the Cancer Patients

Practical medical examinations of astronauts in recent years have revealed that space travel involves a number of health risks: osteoporosis, reduced lung volume, loss of muscle density, exposure to radiation, and so on. However, conversely, space can also bring unexpected therapeutic solutions. This is what biologists have discovered by observing that, immersed in microgravity, the cancer cells are unable to recognize and assemble, and eventually become neutralized.

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Since 2014, Joshua Choi, a biomedical engineering researcher at the University of Technology Sydney, has been studying the effects of microgravity on the physiology and cells of the human body. Early next year, he and his research team will visit the ISS to test a new method of treating cancer based on microgravity.

According to Chou, his research was inspired by a conversation he had with the late Stephen Hawking. During the conversation, Hawking noticed that nothing in the Universe defies gravity. Later, when a friend of Cabbage was diagnosed with cancer, he remembered what Hawking said and began to wonder, " What would happen to cancer cells if we removed them from gravity? ".

Cancer cells accustomed to evolve in a classical gravitational environment

In simple terms, cancer is a disease in which cells begin to divide uncontrollably and spread to certain parts of the body. Cancer cells do this by coming together to form a solid tumor in the body, which then develops until cells invade healthy tissues - such as the heart, lungs, brain, liver, pancreas, etc.

The process by which cancer develops and spreads would seem to indicate that there is a way in which cells are able to detect and gravitate together to form a tumor. However, researchers in biomedicine know that mechanical forces are the only way for cancer cells to detect each other, and that these forces have evolved to operate in a gravitational environment.

Immerse cancer cells in microgravity to block their evolution

This prompted Chou to think of ways in which the absence of gravity could prevent cancer cells from dividing and spreading. He and his team have tested the effects of microgravity on cancer cells in their laboratory. To do this, one of his students created a device that essentially consists of a container the size of a tissue box with a small centrifuge inside.

The researchers used a rotating arm centrifuge to recreate microgravity conditions. Credits: Sascha Kopp et al.

The cells of different cancers are contained in a series of tubes inside the centrifuge, which then rotates them until they experience the sensation of microgravity. As Chou said, the results have been rather encouraging. " Our work has shown that, in a microgravity environment, 80 to 90% of the cells of the four types of cancer tested - ovary, breast, nose and lung - were deactivated and then killed ."

a) Under the effect of microgravity, thyroid cancer cells are forced to rearrange their cytoskeleton. b) Culture of cancer cells under normal conditions; the cancerous tissue formed is dense. c) Cultivation of cancer cells in microgravity; the cancerous tissue formed is loose, porous and weakly bound. Credits: Sascha Kopp et al.

When subjected to microgravity conditions, the cancer cells were unable to detect themselves and therefore had a hard time getting together.

Towards in situ confirmation of results ... And the development of new cancer therapies

The next step, which will take place early next year, will be for the team to send their experience in the ISS aboard a space module specifically designed for this purpose (SpaceX will provide launch services). Chou and his colleagues will spend the duration of the experiment (seven days) in the field, where they will follow the progress of the experiment and will perform live cell imaging via data sources.

Joshua Chou, holding the experimental prototype that will be sent to the ISS next year. Credits: Sissy Reyes

Once the experiment is over, the cells will be frozen for their return trip to Earth. Chou and his colleagues will then examine them to look for genetic modifications. If the results on board the ISS confirm what Chou and his team discovered in the laboratory, he hopes they will be able to develop new treatments that can have the same effect as microgravity and neutralize the ability of cancer cells to to detect oneself.

Ideally, these treatments would not be a cure but could complement existing cancer treatment regimens. Combined with drugs and chemotherapy, treatments derived from this research would effectively slow the spread of cancer in the human body, making conventional treatments more effective and short-lived (and less expensive as well).


Wednesday, 4 December 2019

If they exist, cosmic strings would be much harder to detect than expected

Following the Big Bang, the Universe has undergone several phase transitions that have resulted in broken symmetry of the physical laws. According to some cosmological models, some of these breaks in symmetry would have resulted in the formation of particular cosmic structures at the meeting point of unstable regions of the Universe; these structures are called topological defects, and cosmic strings are one of them. Cosmologists initially thought that signatures of these linear energy structures could be detected in the cosmic microwave background. However, recently, physicists have shown that these signatures would be too weak for their detection to be possible.

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Cosmic strings are hard to imagine, according to Oscar Hernández, a physicist at McGill University in Montreal. " Have you ever walked on a frozen lake? Have you noticed any cracks in the ice? It's still pretty solid, but cracked, "he says. These cracks are formed by a phase transition process similar to that of cosmic strings.

Topological defects predicted by physics beyond the Standard Model

Imperfect meeting points on the surface of a frozen lake form long cracks. In the structure where space and time intersect, they form cosmic strings, if the underlying physics is correct.

Researchers believe that in space, some fields determine the behavior of forces and fundamental particles. The first transition phases of the Universe gave birth to these fields. Today, these points of intersection between fields would appear as infinitely thin lines of energy across space.

Several simulations have shown, if they exist well, the distribution of the cosmic strings during the evolution of the Universe. These topological defects are provided by many theoretical models. Credits: Nature

Most physicists think that the standard model is incomplete. " Many extensions of the standard model naturally lead to cosmic strings after inflation. So, what we have is an object that is predicted by many models. Therefore, if they do not exist, all these models are excluded.

Cosmic strings: they would be impossible to detect in the cosmic microwave background

Hernández and Razvan Ciuca of Marianopolis College in Westmount, Quebec, had previously argued that a convolutional neural network - a powerful type of pattern search software - would be the best tool for locating string evidence in the CMB.

Assuming a perfect and noise-free CMB card, they wrote in a separate article in 2017, a computer using this type of neural network should be able to find cosmic strings even if their energy level (or "voltage") is remarkably low.

But in this new article published on the arXiv server , they showed that in reality, it is almost impossible to provide enough CMB data for the neural network to detect these potential strings. Other brighter microwave sources obscure the CMB and are difficult to disentangle completely. Even the best microwave instruments are imperfect, with limited resolution and random fluctuations in the accuracy of recording from one pixel to another.

They found that all these factors, and more, added to a level of information loss that no current or planned CMB recording and analysis method could ever overcome. This method of chase cosmic strings is a dead end. This does not mean that everything is lost, however.

A new method for detecting cosmic strings

A new method based on measurements of the expansion of the universe in all directions, in old parts of the Universe, could work. This method - called 21-centimeter intensity mapping - does not rely on the study of individual galaxy motions or on accurate CMB images.

Instead, it is based on measurements of the rate at which hydrogen atoms move away from the Earth, on average, in all parts of deep space. This method should be able to provide sufficiently constrained data to restart the hunt for cosmic strings.


Information Theoretic Bounds on Cosmic String Detection in CMB Maps with Noise
Razvan Ciuca1  Oscar F. Hern´andez1,2†

1Department of Physics, McGill University, 3600 rue University, Montr´eal, QC, H3A 2T8, Canada

2Marianopolis College, 4873 Westmount Ave.,Westmount, QC H3Y 1X9, Canada


Monday, 2 December 2019

Unusual radio variations suggest the existence of a new type of binary star system

In current models, binary star systems generally describe couples involving giant stars with white dwarfs or stars like our Sun. In these systems, the smaller companion emits electromagnetic bursts under the gravitational effect of the giant star. Recently, astrophysicists have detected, in the Milky Way, a binary system involving a giant star and an undetermined companion, the couple not responding to the classical properties of such systems. Given the data collected so far, it could be a whole new class of binary system.

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After observing part of the southern hemisphere sky near the constellation Altar for about two months using MeerKAT, a radio telescope based in the Karoo Desert in South Africa, astrophysicists have noticed something strange. The radio emission of an object illuminated by a factor of three, about three weeks of observation. Intrigued, they continued to look at the object and followed the observations of other telescopes. They discovered that the unusual object came from a system of binary stars in the Milky Way.

The results of the study were published in the journal MNRAS. This is the first time that MeerKAT has discovered a "transient source" - an unstable object that is undergoing a significant change in brightness. In view of his name, MKT J170456.2-482100, he was found in the first observed field with the telescope, which means that it is likely to be the tip of an iceberg of transient sources waiting to discovery.

Luminosity variations detected thanks to the collaboration of several telescopes

The researchers began by matching the source to the position of a star, called TYC 8332-2529-1, about 1800 light-years from Earth. Because this star is brilliant, they had predicted that a number of different optical telescopes, detecting visible light rather than radio waves, would have already observed it in the past. And fortunately, this turned out to be the case, allowing them to use these data to learn more about this giant star (2.5 solar masses).

Graphic and images showing radio emission variations observed by astrophysicists. Credits: LN Driessen et al. 2019

Some of the optical telescopes, including ASAS, KELT and ASAS-SN, have provided more than 18 years of star observations. These revealed that the brightness of the star changed over a period of 21 days. Astrophysicists used the SALT telescope to obtain the optical spectra of the star. This can be used to determine the chemical elements present in the star, as well as the presence of a magnetic field.

In addition, they allow scientists to know if a star is moving, because the movement causes the shift of spectral lines (Doppler shift). Spectra revealed that the star had a magnetic field and gravitated around a companion star every 21 days.

A stellar companion of unknown nature

However, only a very weak signature of the companion star is visible. This suggests that the companion must be of less mass than the giant star, with however 1.5 solar masses. So, what could this companion be? A white dwarf may seem likely, as they are often part of binary star systems like this one. However, most have a lower mass than the companion observed.

The radio emission itself could be caused by the magnetic activity of the giant star, similar to a solar flare but much brighter and more energetic. However, these eruptions are usually observed on dwarf stars rather than on giant stars.

Many binary systems involve a giant star and a white dwarf, so the electromagnetic bursts result from the accretion of matter of the second by the first. But the different data collected show that this is not the case of the newly discovered system. Credits: Pearson Ed

Known star systems associating a giant star and a star similar to the Sun could explain the results obtained, the magnetic activity of the giant star giving rise to light flares. However, that does not suit, because nothing indicates in the spectrum that the binary companion is actually a star similar to that of the Sun.

A new class of binary system?

Ben Stappers, the principal investigator of MeerTRAP, one of the teams working on the project, explains that since the properties of the system do not fit easily with our current knowledge about binary stars, it could represent a source class entirely news. It could be a kind of exotic system never seen before and involving a giant star emitting radiation in orbit around a neutron star.

MeerKAT will continue to observe this source every week for the next four years as the ASAS-SN optical telescope continues to observe the giant star. This will inform the dynamics of this system, how the bursts occur, and ultimately help to understand how it was formed.


MKT J170456.2–482100: the first transient discovered by MeerKAT

L N Driessen, I McDonald, D A H Buckley, M Caleb, E J Kotze, S B Potter, K M Rajwade, A Rowlinson, B W Stappers, E Tremou ...

Monthly Notices of the Royal Astronomical Society,
Volume 491, Issue 1, January 2020, Pages 560–575,
Published: 30 October 2019