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Astronomy

New Evidence from NuSTAR Indicates Supernova Explosions Are Lopsided

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The remnant of the famous 1987A supernova. New evidence from NuSTAR indicates that these cosmic explosions are actually lopsided, shooting the stellar core in one direction, and the rest of the material in another.

New data from NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) indicates that a massive star exploded in a lopsided way, the most convincing evidence yet put forward for this phenomenon.

Most stars aren’t massive enough to fuse heavier elements and eventually fizzle out into white dwarfs. Some, however, have a much more spectacular ultimate fate. The biggest stars in the Universe quickly go through the Periodic Table (in just about 10 million years) up until iron, at which point fusion stops, their core collapses under the effect of gravity, followed by the outer layers which crash into it and rebound with enormous energy, shooting out space and leaving behind an extremely dense stellar remnant (either a neutron star or a black hole). This is what’s called a Type II (or core collapse) supernova and is the final stage in the lifetime of stars which have at least eight times the mass of our Sun.

Stars are of course spherical objects, so you’d expect these explosions would scatter debris about equally in all directions. It seems, however, that the stellar core is extremely unstable just before going supernova, so it isn’t exactly in the center when that happens. This explains why the core blasts off in one direction, while the ejected material mostly goes the other way.

NuSTAR has found evidence of this by studying the remnant of the famous 1987A supernova. Observed by astronomers in 1987, it occurred relatively nearby, in the Large Magellanic Cloud, some 166,000 light-years away (well, nearby in astronomical terms at least). The probe’s instruments have picked up high-energy X-rays emitted by the radioactive isotope titanium-44, most of which were redshifted – a change in the wavelength which indicates something is moving away from the observer. Since titanium-44 is only produced by the supernova, it is clear that the ejecta from the event flying through space away from us. The stellar remnant, on the other hand, which in this case is a neutron star, is thought to have been sent hurdling in the opposite direction. Scientists have suspected Type II supernova explosions are lopsided, but this latest data from NuSTAR seems to finally confirm the hypothesis.

Diagram showing the redshifted glow of titanium-44, which indicates that the material ejected by the supernova is moving away from us.

Diagram showing the redshifted glow of titanium-44, which indicates that the material ejected by the supernova is moving away from us. Image: NASA/JPL-Caltech/UC Berkeley

 

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Astronomy

There Is A Hotly Debatable Twin To The Search For Extraterrestrial Intelligence

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Humanity has been trying to find signals from extraterrestrial civilizations for more than a century. Prior to focusing our eyes and ears on the galaxy and universe beyond, early efforts in the Search for Extraterrestrial Intelligence (SETI) concentrated on listening for messages from within the Solar System.

There have been no alien signals found thus far in these searches. While one signal remains enigmatic, it most likely stems from a human or natural source. But given that we (aside from our stray signals) don’t broadcast ourselves on a regular basis, is it unreasonable to assume that alien civilizations would do the same?

Messaging for Extraterrestrial Intelligence, or METI, is introduced. While it wouldn’t be accurate to state that humanity hasn’t communicated with the cosmos, there have undoubtedly been a few. The Golden Records are audio and visual files that NASA’s Voyager I and Voyager II spacecraft “selected to portray the diversity of life and culture on Earth.” Aliens will probably never find these. However, we have also sent other signals, like the Arecibo Message, which was directed about 21,000 light-years from Earth toward the globular star cluster M13. With only 210 bytes of data, the message was small but contained information about the 4 billion people that lived on Earth at the time, a stick figure of a person, a double helix, and a drawing of the Arecibo radio telescope that sent the message.

The organization METI International was founded in 2015 with the intention of communicating with extraterrestrial civilizations. They delivered a similar message to the super-Earth exoplanet GJ273b in October 2017, which is only 19 light-years away from Earth and may be habitable.

This is where METI becomes a little contentious. A map of the solar system was also included in the Arecibo message, and there are (very speculative) reasons why we might not want to communicate with aliens in our cosmic backyard or even send a return address.

The explanation of the Fermi paradox offered by what is now widely referred to as the “Dark Forest Hypothesis” is one of the reasons METI is controversial.

In short, it looks like the universe is full of planets that might be habitable, but we have never picked up a signal from an alien civilization.

The very dark Dark Forest Hypothesis, which is explained in Liu Cixin’s Remembrance of Earth’s Past trilogy, says that alien civilizations hide their existence because you can’t be sure what other civilizations want. There’s no way for you to know if they are hostile or friendly, or what their intentions are.

It’s possible that you, as a friendly civilization, find an alien civilization that is also friendly and about the same level of development as yours. You know you’re nice, but you don’t know if they’re also calm. Even worse, because of how far away these civilizations are and how long it takes to receive light and signals from them, you have no idea how their society has changed since the signal from them reached yours. In the meantime, they may have made huge technological leaps. This means that even if the planet you are looking at seems peaceful and not too far ahead of yours, everything could have changed by the time the light gets to you.

On top of that, there is the pressure of resources. According to the books, you also know from your own planet that life uses and spreads all the resources it can find. But there are only so many resources in the universe.

You still have to deal with the fact that you don’t know if they know that you are peaceful if you decide that they are peaceful. Since they think or even just suspect that you are bad, it makes sense that they would try to kill you before you could kill them. You could talk to them, just like you can here on Earth, to reassure them even more of your plans. In space, though, it could take hundreds or even thousands of years for your new message to get there. During that time, they could have began an attack to destroy you. With this many red flags, Liu comes to the conclusion that the only smart thing for a civilization that wants to stay alive is to hide in the forest and kill any civilizations that make noise, before they kill you.

Scientists are serious about the idea of hostile aliens, even though the idea became popular in fiction. In 2015, Stephen Hawking started a project to look for alien civilizations. He talked about why it might not be a good idea to say hello back.

According to Space.com, Hawking told the crowd, “We don’t know much about aliens, but we know a lot about humans.” “If you look at history, interactions between humans and less intelligent creatures have often been terrible for them, and interactions between civilizations with advanced and primitive technologies have also been bad for the less advanced.” If someone reads one of our messages, they might be billions of years ahead of us. They will be much stronger if that’s the case, and they might not value us more than we value bacteria.

However, the Dark Forest theory is still a long way from being proven. It is important to think about hostile aliens when deciding whether to contact other species and who should make that decision. David Brin, an American author and scientist, asked “whether small groups of zealots should bypass all institutions, peer critique, risk appraisal, or public opinion, to shout ‘yoohoo’ into a potentially dangerous cosmos.”

In a way, the fact that METI exists could be used to show that the Dark Forest Hypothesis is wrong. Let’s say there are very advanced societies out there. Assuming that some people in these advanced civilizations have access to advanced broadcast technology is a reasonable thing to do. Another reasonable guess is that if they were that advanced, they would have built this civilization with science instead of magic.

The civilizations would probably gather information about other star systems in the same way that we do, unless they have a good reason for not wanting to know about life beyond their own planet. Assuming that this information and broadcast technology aren’t somehow limited across all civilizations, there must be some people who would be crazy enough to try to get in touch with other civilizations. While obviously speculating wildly, it’s possible that an alien METI species that likes to take risks might try to warn other, younger civilizations about how the universe is like a dark forest. Also, we haven’t heard from these actors, which could mean that the long silence has a different cause than the Dark Forest Hypothesis.

That, or the METI problem, might only happen in new civilizations that send out messages every so often before we learn about the universe’s dark side and do everything we can to stay quiet.

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Astronomy

The exciting Lunar Standstill will be streamed live from Stonehenge

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People are very interested in Stonehenge, which is one of those famous landmarks. It is very clear that it lines up with the sun at the solstices, but no one is sure what the monument is for. But over the next few months, scientists will look at a different kind of alignment: some stones may be lined up with the lunar standstill.

In the sky, things move around. The sun moves around during the year because the planet is tilted with respect to its orbit. This means that the times when it rises and sets are often different. Stonehenge is set up so that the first rays of dawn on the summer solstice and the last rays of sunset on the winter solstice both pass through the middle.

But outside the stone circle are the so-called station stones, whose purpose is unknown. They don’t seem to be linked to the sun, but to the moon. The position of the moonrise and moonset changes because the moon’s orbit is tilted relative to the earth. This is similar to how the sun moves. But it doesn’t happen every year. The cycle goes around and around for 18.6 years.

When the Moon is at the fullest point of its cycle, it moves from 28.725 degrees north to 28.725 degrees south in just one month. The next one won’t happen until January 2025. This time is called the major lunar standstill (lunistice). So, scientists will be going to Stonehenge several times over the next few months, even during the major standstill, to figure out how the monument might line up with our natural satellite.

Talked to Heather Sebire, senior property curator at Stonehenge. “I think the moon in general would have been very important to them.” “And you know, maybe they could do things they couldn’t do other times when there was a full moon because there was more light.”

“They think the lunar standstill might have something to do with this because there are four rocks out in the middle of the ocean that are called “station stones.” Only two of them have been found so far. Together, they form a rectangle, which some people think may have something to do with the setting outside the circle.

When the Moon is in a minor standstill, its distance from the Earth is between 18.134° north and south. It will happen again in 2034.

As archaeologists continue to look into this interesting alignment, Stonehenge wants everyone to join in the fun. As usual, people will be able to enter the circle for the solstice, which this year is the earliest since 1796. However, the next day will be all about the lunistice.

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As the moon rises, the lunar standstill event can only be seen online. You can watch the livestream from the comfort of your own home and wonder with the researchers if this great monument was also lined up with the Moon.

 

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Astronomy

It’s true that the Earth is not orbiting the sun right now

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Some of the diagrams and animations that show how the planets move around the sun are not quite accurate. To be more precise, they are making the planets’ orbits easier to understand so that teachers don’t have to explain barycenters to kids who are still getting used to the idea that Earth isn’t the only planet in the universe.

Most of the time, the way you learn about how planets move around the sun looks like the video below.

But this version is easier to understand. The Sun has about 1,048 times the mass of Jupiter, making it the largest object in the Solar System. However, gravity works both ways. For the same reason that the Earth pulls on itself, you pull on the Earth as well, though it is much smaller.

“Kepler’s third law describes the relationship between the masses of two objects mutually revolving around each other and the determination of orbital parameters,” NASA says.

“Think about a small star that circles a bigger star. The two stars actually move around the same mass center, which is called the barycenter. That’s always the case, no matter how big or heavy the things are. Using a massive planet to measure how fast a star moves around its barycenter is one way that planetary systems linked to faraway stars have been found.

To keep things simple, we say that the planets go around the Sun. But because the Sun has the most mass, the barycenter of the Solar System’s objects is usually close to it. However, because of Jupiter and Saturn’s orbits and effects, it is almost never inside the Sun. The paths look a bit more like the video below, which was made by planetary astronomer and science communicator James O’Donoghue.

Because of this, the Earth is not orbiting a point inside the Sun right now because the barycenter is not there. We are not going around the sun, but that point in space.

“Planets orbit the Sun in general terms,” O’Donoghue says on Twitter, “but technically, they don’t orbit the Sun alone because the gravitational influence of (mainly) Jupiter means planets must orbit a new point in space.”

“The planets do orbit the Sun, of course; we are just being pedantic about the situation,” he said. “The natural thinking is that we orbit the Sun’s center, but that very rarely happens, i.e., it’s very rare for the solar system’s center of mass to align with the Sun’s center.”

Things that are smaller, like planets and their moons, are the same way. The Earth and Moon go around a point about 3,100 miles (5,100 kilometers) from the Earth’s center. This path changes as the moon moves farther away from the earth.

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