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

Sunday, 9 February 2020

Relativistic drag predicted by Einstein is confirmed

Artistic representation of the "reference drag": two stars orbiting each other twisting space and time

A century after it was theorized, astronomers detected the effects of the Lense-Thirring precession - a drag effect of relativistic references - on the movement of a binary star system, composed of a white dwarf and a pulsar.

Vivek Krishnan and colleagues from four countries analyzed twenty years of observational data from the binary to finally confirm this prediction, made by Einstein's general theory of relativity.

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When a massive object spins, general relativity predicts that it pulls space-time around it, a phenomenon known as frame drag.

This phenomenon causes the precession of the orbital movement of gravitationally coupled objects, such as the two bodies of a binary system - precession is the change in the axis of rotation of an object induced by another star, a very subtle gyroscopic effect, but one that can be imagined like a clumsy top that threatens to fall.

Although the trail of references has already been detected by artificial satellite experiments in the Earth's gravitational field, in these cases the effect is tremendously small and difficult to measure. More massive objects, such as white dwarfs or neutron stars, offer a better opportunity to observe the phenomenon under much more intense gravitational fields.

Artistic representation of a rapidly rotating neutron star and a white dwarf dragging the fabric of space-time around its orbit.


Vivek Krishnan and his colleagues observed PSR J1141-6545, a young pulsar spinning rapidly in a tight orbit around a huge white dwarf.
The pulsar is located 10,000 to 25,000 light-years from Earth in the constellation Musca (the fly), which is near the famous Southern Cross constellation.

A pulsar is a fast-spinning neutron star that emits radio waves along its magnetic poles. (Neutron stars are corpses of stars that died in catastrophic explosions known as supernovas; the gravity of these remnants is powerful enough to crush protons together with electrons to form neutrons.)

PSR J1141-6545 circles a white dwarf with a mass about the same as the sun's. White dwarfs are the superdense Earth-size cores of dead stars that are left behind after average-size stars have exhausted their fuel and shed their outer layers. Our sun will end up as a white dwarf one day, as will more than 90% of all stars in our galaxy.

The pulsar orbits the white dwarf in a tight, fast orbit less than 5 hours long, hurtling through space at about 620,000 mph (1 million km/h), with a maximum separation between the stars barely larger than the size of our sun,

They measured the arrival times of the pulses - a pulsar flashes as if it were a cosmic beacon - with an accuracy of 100 microseconds, over a period of almost twenty years, which allowed them to identify a long-term deviation in orbital parameters.

After eliminating other possible causes of this orbital drift, the team concluded that it is the result of the Lense-Thirring precession (Josef Lense [1890-1985] and Hans Thirring [1888-1976]) due to the rapid rotation of the white dwarf's companion.

These results confirm the prediction of general relativity and allowed the authors to improve the accuracy of the calculations of the speed of rotation of the white dwarf.


Article: Lense-Thirring frame dragging induced by a fast-rotating white dwarf in a binary pulsar system

Authors: Vivek Venkatraman Krishnan, M. Bailes, W. van Straten, N.Wex, PCC Freire, EF Keane, TM Tauris, PA Rosado, NDR Bhat, C. Flynn, A. Jameson, S. Osowski

Magazine: Science

Vol .: 367, Issue 6477 pp. 577-580

DOI: 10.1126 / science.aax7007

Friday, 7 February 2020

SpaceX launches its online space launch reservation service. Prices start at a million dollars…

SpaceX has launched a new online booking tool. The service, already announced last year by the company, plans to mainly operate the most successful launcher so far, the Falcon 9. The prices for the “space carpooling” services that SpaceX offers on its website start at 1 million dollars for payloads up to 200 kg, with an additional cost of 10,000 dollars per additional kg.

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The selection tool asks to specify the desired orbit (synchronous with the Sun, low Earth or polar) as well as the minimum date of preparation (ie the closest at which the payload can be ready). The first dates proposed are in June 2020. The total mass of the load must then be entered in order to obtain an estimate of the cost.

We then access a series of screens where it is possible to add a 15 or 24 inch port if necessary (which largely depends on the volume and mass), as well as to choose the specific rocket on which one wishes to book the flight (from scheduled missions to come).

Home screen of the online booking tool. Credits: SpaceX

Other options include accessories such as port adapters to meet the standard dimensions used by SpaceX, as well as a separation system provided by SpaceX, with on-site fueling options if the spacecraft being dispatched has its own propulsion system. Insurance covering a maximum value of $ 2 million is also offered.

Credits: SpaceX

An instant booking tool

It is important to note that this is not just a simple lead generation form. In fact, once all the options have been selected and it is confirmed that you are not subject to any action or restriction on international arms trafficking (ITAR) imposed by the United States government, the system requests a number credit card to instantly deposit $ 5,000 as a deposit. The rest of the payment can then be made in three installments, after confirmation of the acceptance of your request by SpaceX.

A user guide, which provides more details on the program, including technical requirements, details on environmental testing, legal considerations and much more, is also available online.

Credits: SpaceX

Credits: SpaceX

This reservation system clearly shows how SpaceX is revolutionizing the space sector, in particular by making it more accessible to private companies. Indeed, it becomes almost as easy (as long as you have the necessary funds) to send an object into orbit aboard a reusable rocket as it is to reserve a car. To test the tool (or to book a real launch…), it's Here.

Reservation Link

Tuesday, 4 February 2020

The formation and dynamics of the ice cap of the South Pole of Mars finally explained

Although it has been studied for decades, the red planet still contains mysteries. For many years, a particular structure has caught the attention of planetologists, its origin remaining a mystery: an ice cap, composed of ice water and CO2, covering the South Pole of Mars. Recently, a team of NASA astrophysicists, using simulations, was able to confirm the generally advanced hypothesis to explain the formation and dynamics of this ice structure.

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The main assumption  is that these layers stacked on top of each other during variations in the tilt of the axis of Mars during its orbit around the Sun, and new simulations published in the journal confirm this idea. The ice cap in question is about a kilometer deep and is believed to contain as much CO2 as the Martian atmosphere today, and a combination of factors has produced this unusual layer pattern.

“Usually when you run a model, you don't expect the results to match as closely as you observe. But the thickness of the layers, determined by the model, perfectly matches the radar measurements of satellites in orbit,” explains Peter Buhler, planetologist at NASA's Jet Propulsion Laboratory.

Structural graph of the ice cap of the South Pole of Mars. Credits: PB Buhler et al. 2020

CO2 ice stabilized thanks to the dynamics of Mars

What makes the South Pole ice cap so strange is that it really shouldn't be there - water ice is more thermally stable and darker than CO2 ice, so planetologists would expect that the CO2 ice is destabilized when it is trapped under the water ice.

CO2 ice cycle on the ice cap of the South Pole of Mars. The dynamics of this ice are subject to climatic and atmospheric variations on the planet. Credits: PB Buhler et al. 2020

According to the new model, three factors prevented this from happening: the changing tilt of Mars as it orbits the Sun, the differences in how these two types of ice reflect sunlight, and the change in atmospheric pressure. which occurs when the CO2 ice turns to gas.

Oscillations of the obliquity of Mars responsible for the CO2 ice cap

The "oscillations" of Mars on its axis of rotation would change the amount of sunlight reaching the South Pole, forming CO2 ice during certain periods and sublimating it (by passing it from a solid to a gas) during other periods.

During periods of ice formation, water ice would be trapped alongside the CO2. As sublimation occurs, this more stable ice would remain behind, forming the layers now present at the South Pole of Mars.

(A and D): Graphs showing the variations in mass of CO2 as a function of the variations in obliquity of Mars. (E) Image showing the structure of the ice cap of the South Pole of Mars with comparison between the observations and the authors' model. Credits: PB Buhler et al. 2020

Over time, climate change on the red planet has not resulted in a systematic sublimation of CO2, piling up successive layers of CO2 ice and water ice. Models show that this process changes atmospheric pressure - between a quarter and twice the level it is today - just as Leighton and Murray predicted in the 1960s.

This has been going on for around 510,000 years, suggest the authors - since the last period of extreme solar illumination, when all of the CO2 had been sublimated in the Martian atmosphere. " Our determination of the history of the large pressure fluctuations of Mars is fundamental to understanding the evolution of the planet's climate, including the history of the stability and habitability of liquid water near the surface  " Buhler concludes.


Coevolution of Mars’s atmosphere and massive south polar CO2 ice deposit

P. B. Buhler, A. P. Ingersoll, S. Piqueux, B. L. Ehlmann & P. O. Hayne

Nature Astronomy (2019)

Saturday, 1 February 2020

In a binary system, a rapidly rotating white dwarf carries space-time with it

From black holes to gravitational waves to the effects of gravitational lenses, Albert Einstein's theory of general relativity has made many predictions that have been validated experimentally over time. However, some of these predictions are less known than others. This is the case of the Lense-Thirring effect, which describes a phenomenon of space-time training around very dense objects in very fast rotation. Launched in 2004, NASA's Gravity Probe B satellite made it possible to confirm this phenomenon experimentally in 2011. And recently, astrophysicists have once again been able to confirm the Lense-Thirring effect around a white dwarf as part of a binary system.

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In everyday life, this phenomenon is both undetectable and inconsequential, because the effect is ridiculously small. Detecting the spacetime entrainment caused by Earth's rotation requires satellites such as the $ 750 million Gravity probe B and detecting angular changes in gyroscopes equivalent to one degree every 100 '000 years approximately.

Fortunately, the Universe contains many natural gravitational laboratories where physicists can observe Einstein's predictions in detail. This new study, published in the journal Science , reveals evidence of the Lense-Thirring effect on a much more noticeable scale, using a radio telescope and a unique pair of compact stars rotating around each other. on the other at dizzying speeds.

A white dwarf and a pulsar to confirm the Lense-Thirring effect

The movement of these stars would have made astronomers perplexed at Newton's time, because they move in a distorted space-time, and require the general theory of relativity of Einstein to explain their trajectories. One of his least known predictions of this theory is that rotating bodies carry with them space-time. The faster an object turns and the more massive it is, the more powerful the drive.

White dwarfs are a great place to study this process. They are similar in size to Earth but hundreds of thousands of times more massive. They can also rotate very quickly, up to one revolution per minute. The training caused by such a white dwarf would be about 100 million times more powerful than that of Earth.

Illustration showing the Lense-Thirring effect as part of a white-pulsar dwarf binary system. Credits: Mark Myers / OzGrav ARC Center of Excellence

Twenty years ago, the CSIRO's Parkes radio telescope discovered a unique star pair made up of a white dwarf (the size of Earth but about 300,000 times more massive) and a radio-pulsar. Pulsars are made up of closely related neutrons , which makes them incredibly dense. In addition, they spin much faster than white dwarfs: 150 revolutions / minute for the pulsar studied by the authors.

PSR J1141-6545: an ideal gravitational laboratory for studying general relativity

This means that, 150 times per minute, a beam of radio waves emitted by this pulsar scans our point of observation here on Earth. Astrophysicists can use it to map the trajectory of the pulsar as it orbits the white dwarf, timing when its pulse arrives at the telescope, and knowing the speed of light. This method revealed that the two stars orbit each other in less than 5 hours.

This pair, officially called PSR J1141-6545, is an ideal gravitational laboratory. Since 2001, researchers have used Parkes several times a year to map the orbit of this system, which has a multitude of gravitational effects.

Although PSR J1141-6545 is several hundred quadrillion kilometers (one quadrillion represents a million billion), the data shows that the pulsar rotates 2.54 times per second, and that its orbit varies in space. This means that the plane of its orbit is not fixed, but rotates slowly.

Binary system: the companion star accelerates the rotation of the white dwarf

When pairs of stars are born, the most massive one dies first, often creating a white dwarf. Before the second star dies, it transfers matter to its white dwarf companion. A disc forms when this material falls towards the white dwarf, and over tens of thousands of years, it accelerates the latter, until it makes a complete revolution every few minutes.

Many binary systems involve a giant star and a white dwarf, the latter accreting matter from the former. This accretion leads to an acceleration of the rotation of the white dwarf. Credit: Pearson Ed

In rare cases like this, the second star can then explode as a supernova, leaving behind a pulsar. The rapidly spinning white dwarf carries space-time with it, rocking the pulsar's orbital plane as it moves. This inclination is what astrophysicists have observed through the mapping of the orbit of the pulsar.


Lense–Thirring frame dragging induced by a fast-rotating white dwarf in a binary pulsar system

V. Venkatraman Krishnan, M. Bailes, W. van Straten, N. Wex, P. C. C. Freire, E. F. Keane, T. M. Tauris, P. A. Rosado, N. D. R. Bhat, C. Flynn, A. Jameson1, S. Osłowski

Science  31 Jan 2020:

Vol. 367, Issue 6477, pp. 577-580

DOI: 10.1126/science.aax7007

Thursday, 30 January 2020

Discover these spectacular images of the Sun with the highest resolution ever

The highest resolution image of the Sun’s surface ever taken. | NSO / AURA / NSF

A new telescope specially designed to study the Sun has released its first images, and they are breathtaking. They show the surface of the Sun like never before, revealing the extraordinary details of its surface, convection granules the size of Texas as well as tiny magnetic characteristics (like lines of magnetic field which extend in space).

The telescope that provided these images is the National Science Foundation's Daniel K. Inouye Solar Telescope, located in Haleakalā (Maui), Hawaii.

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His future observations will provide a much broader insight into the wild dynamics of the solar surface and how it affects the Earth. " This is literally the greatest advance in mankind's ability to study the Sun from the ground, since the time of Galilee, " said astronomer Jeff Kuhn of the Institute of Astronomy in Māno, from the University of Hawaii.

These moving spots that you can see in the video below, are called granules . These are the tops of the convection cells in the solar plasma, with hot plasma rising in the middle, then falling down at the edges when it moves outwards and cools. Each granule is extremely large: up to 1600 km in diameter. In comparison, the US state of Texas is approximately 1,270 kilometers long.

Study magnetic fields to understand more about solar dynamics

These images are of course extraordinary, but scientists are particularly interested in the magnetic fields, twisted and tangled by the plasma, which can cause powerful solar storms, capable of interrupting the electrical networks here on Earth (although such consequences are rare).

However, less powerful solar storms can still impact communication and navigation systems and generate magnificent auroras. But today our understanding and ability to predict space weather is still extremely limited. As a result, scientists hope that this telescope will help them better understand solar phenomena.

" On Earth, we can predict if it will rain almost anywhere in the world in a very precise way, but this is not the case with space weather, " said Matt Mountain of the Association of Universities for research in astronomy, which manages the solar telescope. " What we need is to understand the physics behind space weather, and it starts with the Sun, which the Inouye solar telescope will study in the coming decades, " he said. added.

This is none other than the highest resolution snapshot of the Sun's surface ever taken. Credits: NSO / AURA / NSF

Thanks to its many advanced instruments (some of which are not yet operational), the telescope will be able to measure and characterize magnetic fields precisely, like never before.

These measurements could then teach us more about solar storms and how to detect them before they happen: at the moment, we only get to know about 48 minutes in advance. Scientists hope that improving our understanding of the behavior of magnetic fields, leading to a solar storm, could increase this time to 48 hours.

"It all depends on the magnetic field, " said Thomas Rimmele, director of the Inouye solar telescope. " To unravel the greatest mysteries of the Sun, we must not only be able to clearly see these tiny structures located 150 million kilometers away, but also to measure very precisely the strength and direction of the magnetic field near the surface and to trace its extension in the crown, the outside atmosphere of the Sun, to a million degrees, "he added.

The largest square on the surface of the sun is the entire image taken by the telescope. The enlarged (an area of ​​the first square) is a zoom making 7000 kilometers along its length. The small box in the zoom represents approximately the size of Texas. Finally, the tiny point which is almost invisible, is about the size of Manhattan. Credits: NSO / NSF / AURA

In the coming months, additional instruments will reinforce the already phenomenal power of the telescope.

There will be the near infrared cryogenic spectropolarimeter (CryoNIRSP), which is designed to take measurements of the solar magnetic field beyond the visible solar disk, in the crown. And also the near infrared limited diffraction spectropolarimeter (DL-NIRSP), which will study magnetic fields and their polarization with high spectral and spatial resolution.

“These first images are just the start! Said astronomer David Boboltz of the National Science Foundation's Astronomical Sciences Division." The Inouye solar telescope will collect more information about our Sun during the first 5 years of its life than all the solar data collected since Galileo pointed a telescope to the sun in 1612," he added. . The telescope is expected to be fully completed by June 2020.


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