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Gravitational-wave astronomy is very different from that of electromagnetic light. While gravitational waves are faint and difficult to detect, they also pass through matter with little effect. In essence, the material universe is transparent to gravitational waves. This makes gravitational wave astronomy a powerful tool when studying the universe. But it’s still in the early stages, and there is much to learn about how gravitational waves behave.

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Gravitational Lenses. Source: Caltech

Take, for example, gravitational lensing. It occurs when light from a distant object such as a quasar is deflected slightly as it passes near a galaxy or other massive object. The gravitational curvature created by the galaxy’s mass acts as a lens, which can focus the quasar light and produce multiple quasar images. This effect occurs because light travels through space and time, so when spacetime is warped, so is the path of light.

But gravitational waves are different. Rather than photons traveling through space, gravitational waves are ripple of spacetime in spacetime. So can they be deflected or lensed similar to light? Einstein’s theory of relativity predicts they can be. A warping of space changes the way gravitational waves propagate, so they are also deflected. This effect has never been observed, but a new study has combed LIGO and Virgo data looking for it.

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Animated illustration of a gravitational wave. Credit: ESA–C.Carreau

The team looked for several effects of gravitation lensing on the black hole merger signals detected by LIGO and Virgo, such as identical mergers coming from slightly different sources, or an interference pattern in gravitational waves that would be caused by two images of the merger reaching Earth at slightly different times.

In the latest data run containing 36 merger events, the team found no evidence of lensed gravitational waves. That’s not too surprising, given the sample size. But the team has shown it is possible given current technology. As new gravitational wave observatories such as LISA are built, lensed gravitational waves will either be detected, or we will have to re-examine Einstein’s theory.

This kind of study has tremendous potential to enhance our understanding of the universe. Currently, the gravitational lensing of light lets us see more distant objects than we would otherwise, and lets us measure aspects of cosmology such as the expansion of the universe. But light can be obscured or dimmed by diffuse gas and dust between galaxies. Gravitational waves aren’t limited in this way, so gravitational lensing could allow us to make precise
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Should We Send Humans to Venus?

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NASA is preparing to send humans back to the Moon with the Artemis missions in the next few years as part of the agency’s Moon to Mars Architecture with the long-term goal of landing humans on the Red Planet sometime in the 2030s or 2040s. But what about sending humans to other worlds of the Solar System? And, why not Venus? It’s closer to Earth than Mars by several tens of millions of kilometers, and despite its extremely harsh surface conditions, previous studies have suggested that life could exist in its clouds. In contrast, we have yet to find any signs of life anywhere on the Red Planet or in its thin atmosphere. So, should we send humans to Venus?

“Yes, we should send humans to Venus,” Dr. Paul Byrne, who is an Associate Professor of Earth, Environmental, and Planetary Sciences at Washington University in St. Louis, tells Universe Today. “But first, let’s talk about what ‘sending humans to Venus’ actually means. The surface of Venus is hellish, so nobody would last long there nor volunteer to go. Above the clouds, the temperature and pressure are almost like a nice spring day here on Earth, so aside from tiny sulphuric acid cloud droplets you’d be okay (with a breathing apparatus).”

These “hellish” conditions that Dr. Byrne alludes to are the extreme conditions across the surface of Venus, including surface pressures 92 times that of Earth’s surface and average surface temperatures of approximately 464 degrees Celsius (867 degrees Fahrenheit). In contrast, Earth’s average surface temperatures are a calm 15 degrees Celsius (59 degrees Fahrenheit). These extreme pressures and temperatures have made landing on the surface of Venus even more difficult, as the former Soviet Union continues to be the only nation to have successfully landed on Venus’ surface, having accomplished this feat with several of their Venera and Vega missions. However, the longest mission duration for the lander was only 127 minutes (Venera 13), which also conducted the first sound recording on another planet.

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Color images taken by the Soviet Union’s Venera 13 lander on the surface of Venus on March 1, 1982, with the lander surviving only 127 minutes due to Venus’s extreme surface conditions. (Credit: NASA)

“If we were to send humans to Venus, they’d be going in a spacecraft that would fly by the planet en route somewhere else,” Dr. Byrne tells Universe Today. “If we were to one day send humans actually to Venus itself for science and engineering purposes, then a cloud-based habitat is the way to go. Getting humans onto the Venus surface is going to require so much technology and expense that, for the foreseeable future, I don’t think anyone will think it worth doing.”

A 2015 study presented at the AIAA Space and Astronautics Forum and Exposition outlined a NASA study for the High Altitude Venus Operational Concept (HAVOC) mission that would involve a 30-day crewed mission using an airship equipped with solar panels within the upper atmosphere of Venus. This is because Venus’ upper atmosphere at approximately 50 kilometers (30 miles) above the surface exhibits much more hospitable conditions, including temperatures between 30 to 70 degrees Celsius (86 to 158 degrees Fahrenheit) and pressures very close to that of Earth. However, Dr. Byrne refers to HAVOC as an “unbelievably expensive concept”.

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Artist rendition of proposed habitable airships traversing Venus’ atmosphere, which has been proposed as the High Altitude Venus Operational Concept (HAVOC) mission. (Credit: NASA)

As for using Venus while en route to another location in the Solar System, Venus has been used on several occasions to slingshot spacecraft to the outer Solar System as well as for exploration of the inner Solar System, such as Mercury and the Sun. For example, NASA’s Galileo and Cassini spacecraft used gravity assists

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We Should Hit Peak Solar Activity Next Year

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You may be familiar with the solar cycle that follows a 22 year process shifting from solar minimum to maximum and back again. It’s a cycle that has been observed for centuries yet predicting its peak has been somewhat challenging. The Sun’s current cycle is approaching maximum activity which brings with it higher numbers of sunspots on its surface, more flares and more coronal mass ejections. A team from India now believe they have discovered a new element of the Sun’s magnetic field allowing them to predict the peak will occur early in 2024.

The Sun is a gigantic sphere of plasma or electrically charged gas. One of the features of plasma is that if a magnetic field passes through it, the plasma moves with it. Conversely if the plasma moves, the magnetic field moves too. This magnetic field is just like Earth and is known as a dipole magnetic field. You can visualise it if you can remember your school science days with a bar magnet and iron filings.

A dipole magnetic field has two opposite but equal charges and at the start of the Sun’s cycle the field lines effectively run from the north pole to the south. As the Sun rotates, with the equator rotating faster than the polar regions, then the plasma drags the magnetic field lines with it, winding them tighter and tighter.

The field lines become stretched causing the magnetic field to loop up and through the visible surface of the Sun. This localised event prevents the convection of super heated gas from underneath and appears as a cooler area of the surface which appears dark. As the solar cycle starts, these sunspots appear around the polar regions and slowly migrate toward the equator as it progresses with peak activity occurring when the sunspots fade away as we head toward the start of another cycle. 

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Image of sunspots (Credit : NASA Goddard Space Flight Center // SDO)

On occasions the magnetic field of sunspots are disrupted and we can experience flares or coronal mass ejections hurling vast amounts of charged particles out into space. If they reach us here on Earth they give rise to the beautiful aurora displays but they do also have a rather negative impact to satellites, power grids and telecommunications systems.

Deep inside the Sun, a dynamo mechanism is driving all this. It is created by the energy from the movement of plasma and it is this that is responsible for the flipping of the Sun’s magnetic poles where the north pole becomes south and the south pole becomes north which happens every 11 years or so. It’s another aspect of the solar cycle.

It’s been known since the 1930’s that the rate of rise the sunspot cycle relates to its strength with stronger cycles taking less time to reach peak. In the paper published in the Monthly Notices of the Royal Astronomical Society Letters; Priyansh Jaswal, Chitradeep Saha and Dibyendu Nandy from the Indian Institutes of Science Education and Research announced their findings. They discovered that the rate of decrease in the Sun’s dipole magnetic field also seems to relate to the rise of the present cycle.

The team have looked back through archives and have shown how the observation of the dipole decrease rate along with observations of sunspots can predict the peak of activity with better accuracy than before. They conclude the current cycle is expected to peak somewhere between early 2024 and September next year. Being able to better predict the peak of activity will help understand the likely intensity of space weather events here on Earth providing us more warning to be able to prepare.

Source : Solar activity likely to peak next year, new study suggests

The post We Should Hit Peak Solar Activity Next Year appeared first on Universe Today.

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The Solar Radius Might Be Slightly Smaller Than We Thought

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Two astronomers use a pioneering method to suggest that the size of our Sun and the solar radius may be due revision.

Our host star is full of surprises. Studying our Sun is the most essential facet of modern astronomy: not only does Sol provide us with the only example of a star we can study up close, but the energy it provides fuels life on Earth, and the space weather it produces impacts our modern technological civilization.

Now, a new study, titled The Acoustic Size of the Sun suggests that a key parameter in modern astronomy and heliophysics—the diameter of the Sun—may need a slight tweak.

The study out of the University of Tokyo and the Institute of Astronomy at Cambridge was done looking at data from the joint NASA/ESA Solar Heliospheric Observatory (SOHO’s) Michelson Doppler Imager (MDI) imager. The method probes the solar interior via acoustics and a cutting edge field of solar physics known as helioseismology.

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A cutaway diagram of the Sun. NASA/ESA/SOHO

‘Hearing’ the Solar Interior

How can you ‘hear’ acoustic waves on the Sun? In 1962, astronomers discovered that patches on the surface of the Sun oscillate, or bubble up and down, like water boiling on a stove top. These create waves that ripple in periodic 5-minute oscillations across the roiling surface of the Sun.

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A view of the Sun, courtesy of SOHO’s MDI instrument. Credit: NASA

What’s more, astronomers can use what we see happening on the surface of the Sun to model the solar interior, much like terrestrial astronomers use seismic waves traveling through the Earth to model its core. Thanks to helioseismology, we can even ‘see’ what’s going on on the solar farside, and alert observers of massive sunspots before they rotate into view.

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Solar farside modeling using helioseismology. Credit: NSF/GONG

The study looked at p-mode waves as they traversed the solar interior. Previous studies relied on less accurate f-mode waves, which are surface waves considerably shorter than the solar radius.

The study defines the solar radius (half the diameter) as 695,780 kilometers… only slightly smaller than the generally accepted radius of 696,000 kilometers obtained by direct optical measurement. This is only smaller by a few hundredths of a percent, or 100-200 kilometers.

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An artist’s conception of SOHO in space. Credit: ESA/SOHO

The solar radius is a deceptively simple but crucial factor in astronomy. The Sun is a glowing ball of hydrogen and helium plasma without a distinct surface boundary. The photosphere—the glowing visible layer we see shining down on us on a sunny day—is what we generally refer to as the surface of the Sun.

The Solar Radius: A Brief
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