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Betelgeuse Is Brightening Again – Universe Today

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The latest observations of Betelgeuse show that the star is now beginning to slowly brighten. No supernova today! Nothing to see, better luck next time.

Despite some of the hype, this behavior is exactly what astronomers expected. Betelgeuse is a very different star from our Sun. While our Sun is a main-sequence star in its prime of life, Betelgeuse is a red giant star on the verge of death. But the death of a star is not a simple process.

The rate of energy production by nuclear fusion in a star. Credit: R J Hall

Stars shine so brightly and for so long because of a delicate balance of gravity and nuclear fusion. Gravity would like to collapse a star under its weight. Without nuclear fusion, gravity would crush a star into a white dwarf, neutron star, or black hole. But the crushing pressure gravity creates allows hydrogen in the star’s core to fuse into helium. The process is known as the proton-proton chain (or pp-chain) and combines four hydrogen nuclei into one helium nucleus. About 3% of the original mass is converted to energy in the form of gamma rays. This energy heats the core even further, letting it push back against gravity.

For stars larger than the Sun, another fusion process known as the CNO cycle kicks in. CNO stands for Carbon-Nitrogen-Oxygen because the process fuses helium into those three elements. This process is why those three elements are the most abundant in the universe except for hydrogen and helium.

Illustration of a CNO cycle. Credit: Antonio Ciccolella

While both the pp-chain and CNO cycle can occur at the same time within a star, over time the CNO cycle increases as hydrogen become more scarce and helium more abundant. Since the CNO cycle releases more energy at a faster rate than the pp-chain, this means a star’s temperature increases over time. We see this gradual heating in our own Sun. By the time the CNO cycle dominates in a star, it’s core is so hot that the outer layers of a star swell and expand.

This is the stage Betelgeuse is in now. For millions of years, it was a main-sequence star of about 20 solar masses. But it is now fusing helium so furiously that it has bloomed into a red supergiant. Betelgeuse is running out of fuel, and in the end, gravity will win. It’s only a matter of time.

Betelgeuse before and after dimming
This comparison image shows the star Betelgeuse before and after its unprecedented dimming. The observations, taken with the SPHERE instrument on ESO’s Very Large Telescope in January and December 2019, show how much the star has faded and how its apparent shape has changed.

But that time isn’t necessarily soon. Betelgeuse has enough helium to stay in the red supergiant stage for about 100,000 years. Even after it runs out of helium, it will be able to fuse carbon into heavier elements for about a millennium. After that things will change fairly quickly. When it runs out of carbon it will try fusing heavier and heavier elements for about a year. Then its core will collapse, Betelgeuse will become a supernova, and we will finally get our show.

As best we can tell, Betelgeuse is still deep in the red supergiant phase of its life. Even though it has dimmed significantly of recent, it isn’t on the verge of exploding. The gradual dimming and brightening we see suggest that it won’t be exploding in our lifetimes. It suggests that the core of Betelgeuse is still chugging away at a steady pace.

The brightness of Betelgeuse over the years. Credit: AAVSO

The changing brightness of Betelgeuse is due to a process known as convection. The upper layers of the star are heated by the core, and this generates a flow of hotter and cooler regions. Material in the interior is heated and rises to the surface. It then cools and sinks into the star, and the cycle continues. Convection happens in the outer regions of most stars, including our Sun. On the surface of the Sun, these convection regions are known as granules, and they are typically the size of Texas. That sounds large, but for the Sun that’s smaller than most sunspots. So even though the Sun has bright hot regions and dimmer cool regions, they are so small compared to the Sun’s surface there isn’t an overall change in solar luminosity.

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A simulation of convection in Betelgeuse.

But the outer layer of Betelgeuse is much less dense than that of the Sun. It is even less dense than Earth’s atmosphere. It’s basically a thin soup of glowing gas. That means the convection regions on Betelgeuse can be huge. A single region can cover a large part of the star. When one of those regions rises to the top, Betelgeuse gets brighter, and when it cools the star dims. Betelgeuse is starting to brighten because hot material is convecting to its surface. This is normal for Betelguese and is likely the way things will be for millennia.

So no boom today. But boom someday. Sooner or later…Boom!

Reference: Edward Guinan, et al. “The Fall and Rise in Brightness of Betelgeuse

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STEVE appears over Canada during 'surprise' solar storm – Livescience.com

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In the dark of Sunday night and Monday morning (Aug. 7 and 8), a surprise solar storm slammed into Earth, showering our planet in a rapid stream of charged particles from the sun. The resulting clash of solar and terrestrial particles in Earth‘s atmosphere caused stunning auroras to appear at much lower latitudes than usual — and, in southern Canada, triggered a surprise cameo from the mysterious sky phenomenon known as STEVE.

Alan Dyer, an astronomy writer and photographer based in southern Alberta, Canada, caught the wispy ribbons of green and violet light on camera as they shot through the sky.

“STEVE lasted about 40 minutes, appearing as the … aurora to the north subsided,” Dyer wrote on Twitter (opens in new tab) on Aug. 8. “STEVE was ‘discovered’ here so he likes appearing here more than anywhere else!”

Related: Earliest documented aurora found in ancient Chinese text

As Dyer noted, the strange sky glow called STEVE was first described by citizen scientists and aurora hunters in northern Canada in 2017. STEVE is typically composed of an enormous ribbon of purplish light, which can hang in the sky for an hour or more, accompanied by a “picket fence” of green light that usually disappears within a few minutes. 

The glowing river of light may look like an aurora, but it’s actually a unique phenomenon that was considered “completely unknown” to science upon its discovery. Today, scientists have a slightly better idea of what’s going on. 

STEVE (short for “strong thermal velocity enhancement”) is a long, thin line of hot gas that slices through the sky for hundreds of miles. The hot air inside STEVE can blaze at more than 5,500 degrees Fahrenheit (3,000 degrees Celsius) and move roughly 500 times faster than the air on each side of it, satellite observations have shown.

Whereas the northern lights occur when charged solar particles bash into molecules in Earth’s upper atmosphere, STEVE appears much lower in the sky, in a region called the subauroral zone. That likely means solar particles aren’t directly responsible for STEVE, Live Science previously reported. However, STEVE almost always appears during solar storms like Sunday’s, showing up after the northern lights have already begun to fade.

One hypothesis suggests that STEVE is the result of a sudden burst of thermal and kinetic energy in the subauroral zone, somehow triggered by the clash of charged particles higher in the atmosphere during aurora-inducing solar storms. However, more research is needed to uncover the true secrets of STEVE. In the meantime, we can simply bask in its otherworldly glow and wave back at its twinkling green fingers.

Originally published on Live Science.

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Perseid meteor shower: when to catch it in Manitoba | CTV News – CTV News Winnipeg

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The peak of a spectacular space light show is expected to happen by the end of the week.

The Perseid meteor shower is expected to be at its best and brightest the night of Aug. 12 going into the morning of Aug. 13.

Scott Young, an astronomer at the Manitoba Museum, said this is an annual event that will produce dozens of shooting stars throughout the night.

“Every meteor is a piece of dust from outer space that is crashing into the earth at tremendous speed and basically vaporizing in a poof and a flash of light, and that it is what we see as a meteor,” he said. “On certain nights of the year, the earth in its orbit around the sun actually goes through a cloud of dust, sort of like an interplanetary dust bunny, essentially, and all that dust hits on the same night … and so we are basically crashing through the dust left behind by a comet.”

The cloud of dust was left behind by the comet Swift-Tuttle, which last passed by the earth in 1992. Since then, the meteor shower has reached its peak between Aug. 11 and 13.

For those who are looking to enjoy the meteor show, Young suggests people get away from city lights, especially this year as the shower also coincides with a full moon.

“The moon can wash out those fainter meteors, and also if you are in the city, city lights will also wash out those fainter meteors. If you want to see the best show, you want to go late Friday after midnight, into the early morning hours of Saturday.”

If people can’t see the shower that night, Young says not to worry as the Perseid meteor shower is already happening right now and will continue to the end of August. As long as people are away from bright lights, Young says they should be able to see some shooting stars.

He recommends going to places like Birds Hill Provincial Park to enjoy the shower, but noted if people can find a place that is away from direct light, whether that be a park within the City of Winnipeg, or even a person’s backyard, he suggests people will be able to see something.

Once the meteor shower is over, however, Young does have a cautionary tale to share.

“We get dozens calls of people seeing an interesting rock on the ground and thinking that they’ve found a meteorite. There are no meteorites that will fall and actually land on the ground from this shower. These are little pieces of dust and they completely vaporize in the atmosphere. You might find meteorites out there, but they are very, very rare and so don’t get all excited about every rock that you find after this. The odds are it’s a meteor-wrong and not a meteorite.”

Young said weather-permitting, the Manitoba Museum will livestream the shower on its social media channels.

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NASA’s Hubble Space Telescope captured two festive-looking nebulas – Tech Explorist

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The image shows NGC 248, about 60 light-years long and 20 light-years wide. They are two nebulas, situated to appear as one. The nebulas, together, are called NGC 248.

Initially discovered in 1834 by the astronomer Sir John Herschel, NGC 248 resides in the Small Magellanic Cloud, located approximately 200,000 light-years away in the southern constellation Tucana.

Small Magellanic Cloud is a dwarf galaxy that is a satellite of our Milky Way galaxy. The image is part of a study called Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE).

The dwarf satellite galaxy contains several brilliant hydrogen nebulas, including NGC 248. Intense radiation from the brilliant central stars is heating hydrogen in each nebula, causing them to glow red.

The study’s principal investigator, Dr. Karin Sandstrom of the University of California, San Diego, said“The Small Magellanic Cloud has between a fifth and a tenth of the amount of heavy elements that the Milky Way does. Because it is so close, astronomers can study its dust in great detail and learn about what dust was like earlier in the history of the universe.”

“It is important for understanding the history of our galaxy, too. Most of the star formation happened earlier in the universe, at a time when there was a much lower percentage of heavy elements than there is now. Dust is a critical part of how a galaxy works, how it forms stars.”

The image is part of a study called Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE). The data used in this image were taken with Hubble’s Advanced Camera for Surveys in September 2015.

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