2020
October
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The giant and the dwarf

Size alone is not always the most important factor. Sometimes, large things also orbit small things – because the details of a system matter. Astronomers have now found a real example for this situation in space, about 80 light-years from us, using the TESS telescope.

The discovery published in Nature shows the likely presence of a planet the size of Jupiter orbiting the white dwarf, WD 1856+534, once every 34 hours.

“This planet is roughly the size of Jupiter, but it also has a very short orbital period – one year on this planet is only 1.4 days long, so short that the planet is practically being whipped around its white dwarf star,” says Ian Crossfield, an assistant professor for physics and astronomy at the University of Kansas and a co-author of the article.

A white dwarf is the remnant of a star like our Sun, which expanded to form a red giant and then collapsed again to form a dense, weakly luminous core. White dwarfs have about the circumference of the Earth. The planet named WD 1856 b is thus much larger than what’s left of its star. During this process, a star will normally devour planets in its orbit – but that wasn’t the case for WD 1856 b, which somehow seems to have avoided destruction.

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How the Magellanic Stream was formed

The Milky Way does not travel through the universe alone. It is accompanied on its journey by smaller galaxies. The two largest are the Small Magellanic Cloud and the Large Magellanic Cloud, which are both visible as dusty twin smudges in the southern hemisphere.

When the Magellanic Clouds started orbiting the Milky Way billions of years ago (astronomers are not certain about the timing and the gravitational bond, it’s possible that they are still on their first approach to the Milky Way), an enormous stream of gas known as the Magellanic Stream was ripped out of them. The stream now extends across more than half the night sky. Astronomers, however, cannot explain how the stream became so massive that it contains a billion solar masses, which corresponds to one-tenth of the mass of the LMC.

Astronomers from the University of Wisconsin-Madison and their colleagues have now discovered that a halo made up of warm gas surrounding the Magellanic Clouds is probably acting something like a protective cocoon that shields the dwarf galaxies from the Milky Way’s own halo and accounts for the majority of the mass of the Magellanic Stream. When the smaller galaxies came into an area influenced by the Milky Way, parts of this halo were stretched out and scattered and formed the Magellanic Stream. The researchers published their results on September 9, 2020 in the journal, Nature.

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Deformed disk around the triple star system GW Orionis

Our Solar System is remarkably flat, because all the planets orbit in the same plane. But that’s not always the case, especially not for planet-forming disks around systems made up of multiple stars. GW Orionis, for example, which is located more than 1300 light-years away in the constellation Orion, has three stars and a deformed, broken-apart disk surrounding these stars.

“Our images show an extreme case where the disk is not flat at all, but is deformed and has a slanted ring that has detached from the disk,” says Stefan Kraus, professor for astrophysics at the University of Exeter, who led a study published in the journal Science. The oblique ring is located in the inner part of the disk close to the three stars.

The new study shows that this inner ring contains 30 Earth masses of dust, which might be enough to form planets. “All planets formed within the inclined ring will orbit the star on very oblique orbits. We predict that many planets on oblique, widely separated orbits will be detected in future observation campaigns, for example, with the ELT,” says team member Alexander Kreplin of the University of Exeter. Since more than half of the stars in the sky are born with one or more companions, this produces an exciting prospect: there might be an unknown population of exoplanets that orbit their stars on highly inclined and widely separated orbits.

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Is dark energy hidden in the husks of burned-out stars?

The idea that the expansion of the universe is accelerating is taken as fact today. The cause is a repulsive form of energy, dark energy. But its nature remains a mystery. Now, a team of researchers at the University of Hawai’i in Mānoa have made an interesting prediction in The Astrophysical Journal: dark energy, which is responsible for this accelerated growth, could originate from a giant sea of compact objects spread out in the cavities between galaxies.

Since the mid-1960s, physicists have known that the collapse of stars might not produce true black holes, but instead so-called “GEneric Objects of Dark Energy” (GEODEs). In contrast to black holes, GEODEs fit very well into Einstein’s equations, because they don’t contain singularities. Instead, a rotating layer surrounds a core made from dark energy. From the outside, GEODEs and black holes appear very, very similar. This also applies particularly when the “noise” of their collisions is measured with a gravitational wave detector.

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Signs of life from the clouds of Venus?

Our hot sister planet, Venus, basically has no potential for life on its surface – the pressure and temperature are much too high. Nevertheless, in “The Clouds of Venus,” a team from NASA made an interesting discovery. I was reminded of this when I read a new press release from Cardiff University. Astronomer Jane Greaves and her colleagues have been analyzing Venus’s atmosphere for years and stumbled across an interesting substance: phosphane (older, but chemically incorrect name: phosphine).

On Earth, phosphane, a compound of phosphorus and hydrogen (PH3), is a gas produced predominantly by anaerobic biological sources. The conditions on Venus’s surface are indeed hostile to life, but in the upper layer of clouds – about 53 to 62 kilometers (33 miles to 39 miles) above the surface – the conditions are more moderate. The composition of the clouds, however, is very acidic, and under those conditions, phosphane would be broken down very quickly.

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Panspermia: colonies of bacteria can survive in interplanetary space

Deinococcus radiodurans is one tough bacterium. Neither the detonation of atom bombs nor the terrors of empty space bother it. But could it travel from planet to planet as a stowaway? Imagine microscopically small lifeforms being transported through space and landing on another planet. Bacteria that find suitable conditions for their survival on the new planet could then multiply and spawn life on the other side of the universe. This theory, which is known as “panspermia,” postulates that microbes could travel between planets and spread life throughout the universe. Panspermia has been debated for a long time, because it obviously requires that bacteria survive long trips in space, withstanding vacuum conditions, temperature fluctuations, and radiation.

“The origin of life on Earth is the greatest mystery of humankind. Scientists have taken completely opposite viewpoints on this topic. Some think that life is very rare and developed only once in the universe, while others believe that life can develop on any suitable planet. If panspermia is possible, life must be much more common than we thought before,” says Dr. Akihiko Yamagishi, professor at the University of Pharmacy and Life Sciences in Tokyo and lead researcher of the Tanpopo space mission.

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Milky Way vs. Andromeda: the collision has already begun

It’s inevitable that the Milky Way and the Andromeda Galaxy will one day collide and merge, even though right now there’s still 2.5 million light-years between them. Thus, the light that we see from Andromeda today was emitted from there 2.5 million years ago. The two most massive members of the Local Group are approaching each other at 120 kilometers per second. In three to four billion years (so while our Sun is still alive), up to 1.3 billion stars of the two galaxies will encounter each other. After another maybe three billion years, the merger will produce a gigantic elliptical galaxy, which could be called “Milkomeda” perhaps.

The merger, however, already began a long time ago, as researchers discovered using the Hubble space telescope. In an article published in the Astrophysical Journal, they describe how they studied the area around the actual galaxy, the so-called halo, through a program called AMIGA (Absorption Map of Ionized Gas in Andromeda). To do this, they examined light from 43 quasars – the extremely distant, bright nuclei of active galaxies powered by black holes – located far beyond Andromeda. The quasars are positioned behind different areas of the halo, so the researchers could study several different regions. By focusing on the light from the quasars through the halo, the team could observe how this light interacted with and was absorbed by the Andromeda halo and how this absorption changed in different regions. The immense Andromeda halo apparently consists of thin, ionized gas that does not emit any easily detectable radiation. Therefore, tracing the absorption of light coming from a background source is a better way to study these regions.

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More rogue planets than stars in the Milky Way?

When stars are born, their surroundings are not for the weak or squeamish. Planets have to find their way through a young system that has not yet reached a steady state. If they are unlucky, they will be swallowed up by larger planets – or flung out of the system entirely. Then they become lonely wanderers traversing the universe as ice-cold, rocky hunks that are very difficult to detect.

Nobody knows how many of these so-called “rogue planets” there are, because normal telescopes cannot detect their extremely low energy signatures. And they also can’t be discovered by means of transit events, like with normal exoplanets, because they aren’t orbiting a star.

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