Space Thread


Hall of Fame Member
Oct 9, 2004

'Great Dimming' of Betelgeuse star is solved

Jonathan Amos
Science correspondent
@BBCAmoson Twitter
BBC Science
16th June 2021

Images over time of the star

Astronomers say they've put to bed the mystery of why one of the most familiar stars in the night sky suddenly dimmed just over a year ago.

Betelgeuse, a red supergiant in the constellation of Orion, abruptly darkened in late 2019, early 2020.

The behaviour led many to speculate that it might be about to explode.

But a team using the Very Large Telescope (VLT) in Chile says the cause was almost certainly a giant dust cloud between us and the star.

Even if you can't name many points in the sky, you'll definitely know Betelgeuse by sight. It's the orange dot in the top-left corner of Orion - or bottom-right, if you're viewing the constellation in the Southern Hemisphere.

Close to Earth, relatively speaking, at a distance of about 550 light-years, Betelgeuse is what's known as a semi-regular variable star. It naturally brightens and darkens over a period of roughly 400 days.

But what happened 18 months ago was out of the ordinary. The loss of brightness was far greater than anything previously recorded.

Artwork: In the constellation of Orion (the Hunter), Betelgeuse represents the "right shoulder"

Astronomer Miguel Montargès and colleagues investigated the event with the European Southern Observatory's VLT, one of the most powerful telescopes on Earth. It has the resolution to directly image the surface of Betelgeuse.

The researchers compared pictures before, during and after the dimming, and did some modelling to see what kind of behaviour might give rise to the views obtained.

Two ideas were dominant. Perhaps there was a large cool spot on the surface of the star, because red supergiants like Betelgeuse are known to have very large convective cells that can cause hot spots and cold spots. Or maybe there was a cloud of dust forming right in front of the star as viewed from Earth.

The explanation turns out to be "a bit of both", says colleague Emily Cannon from KU (Katholieke Universiteit) Leuven in Belgium.

"Our overall idea is that there was a cool spot on the star which, because of the local drop in temperature, then caused gas ejected previously to condense into dust," she told BBC News.
"So, the cool spot on the surface would initially make the star look dimmer to us. But then this condensation of dust would add to the rapid drop in brightness of the star."

Betelgeuse is about 15-20 times as massive as the Sun. An object that big is likely to go supernova at some point. So, it wasn't crazy to wonder when this unusual dimming occurred that Betelgeuse might be about to let go in a spectacular explosion.

Emily Cannon said: "I don't think this event means Betelgeuse is going to go supernova anytime soon, even though that would be incredibly interesting and I was kind of wishing it myself!

"We know that red supergiants can display increased mass loss rates, which may indicate there's a later stage in their lives when they are more likely to go supernova. But Betelgeuse we think is a relatively young red supergiant and it probably has a lot more time left."

How much time is that? Tens, even hundreds, of thousands of years is the sort of period astronomers will often quote.

It would be an amazing thing to see; the event would be visible in daylight.

The last supernova observed in our Milky Way Galaxy was Kepler's Star, which was observed in 1604.

Records from astronomers at the time indicate it was visible during the day for over three weeks.

Miguel Montargès' team reports its findings in the journal Nature.



New Member
Feb 15, 2021
Wow, that's amazing! I am actually amazed with stuff that concerns space. I think that the footage are amazing and very clear, it's quite hard to think how they were all captured. That is impressive and nice to look at.
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Hall of Fame Member
Oct 9, 2004

Astronomers work out when the first stars shone

By Pallab Ghosh
Science correspondent
BBC News
24th June 2021

This simulation of what one of the first stars would look like is based on astronomical data. Many of them were more massive than our own Sun and relatively short lived

Astronomers have worked out when the first stars began shining.

They say that this period, known as the "cosmic dawn," occurred between 250 to 350 million years after the Big Bang.

The results indicate that the first galaxies will be bright enough to be seen by Nasa's James Webb Space Telescope, which is set to be launched later this year.

The study is published in the Monthly Notices of the Royal Astronomical Society.

Discovering when the cosmic dawn began has been the life's work of Prof Richard Ellis, from University College London, UK.

He told BBC News: "The Holy Grail has been to look back far enough that you would be able to see the very first generation of stars and galaxies. And now we have the first convincing evidence of when the Universe was first bathed in starlight."

The team analysed six of the most distant galaxies. They were so far away that even with the world's most powerful telescopes they appeared as just a few pixels on the computer screen.

They are also among the earliest to have emerged in the Universe and so, by the time their images are captured by telescopes on Earth, they are seen not long after the Big Bang.

By working out their age, the team calculated the start of the cosmic dawn - when the first stars formed.

Dr Nicolas Laporte, from the Kavli Institute of Astronomy in Cambridge led the analysis.

Annotated view of James Webb

Webb's goal will be to see directly the light coming from the first stars and galaxies

"This is one of the biggest questions in modern cosmology.

This is the first time we have been able to predict from observations when this crucial moment in the history of the Universe occurred."

Dr Laporte said that obtaining the result was a dream come true.

"It is fantastic to think that particles of light have been travelling through space for over 13 billion years and then entered a telescope. The wonderful thing about being an astrophysicist is the ability to time travel and witness the distant past," he explained.

The Universe came into being 13.8 billion years ago in the Big Bang. After an initial flash, it went through a period known as the cosmic dark ages. According to the new study, 250 to 350 million years after the Big Bang, the first stars emerged, bringing light to the cosmos.

Critically, the new analysis also indicates that the first galaxies are bright enough and within the range where they can be seen by the James Webb Space Telescope - the successor to the venerable Hubble Space Telescope.

Astronomers may then be able to witness this crucial moment in the evolution of the Universe directly.

The Very Large Telescope in Chile was one of six telescopes used to determine when the first stars began to shine

Scotland's Astronomer Royal, Prof Catherine Heymans, said she was "so excited" by this prospect.

She told BBC News: "Isn't it just so fantastic that, as humanity, a tiny civilisation on pPanet Earth, we can create a telescope that we can send up into space and we can peer back to the Universe as it was just a couple of hundred million years after the Big Bang!"

Many of the first stars were quite different to our own Sun. They were more massive and burned only hydrogen. But these objects created the next generation of stars that led to the formation of heavier periodic table elements.

Everything except for hydrogen, helium and lithium, is created inside stars when they explode at the end of their lives.

We are, therefore, ultimately made from the stars that were born close to the dawn of the cosmos.

"Because we are ourselves the produce of stellar evolution, we are looking back at our own origin," said Prof Ellis.

The researchers analysed starlight from the galaxies using both Hubble and the Spitzer Space Telescope.

They estimated the age of the galaxies by examining the proportion of hydrogen atoms in the atmosphere of their stars. The older the stars, the greater the proportion of hydrogen atoms.

Distant galaxy
A view from close to the beginning of the Universe. This is one of the galaxies the researchers studied. It is seen just 500 million years or so after the Big Bang. It is so distant that, even seen through the world's most powerful telescopes, it appears pixelated

The team then calculated how far away the galaxies were. Because light from these galaxies takes time to reach us, the further away they are, the further back in time astronomers are observing them.

Because the six galaxies the team studied are at the limits of objects that can be observed by telescopes, they are also among the earliest known.

The team needed 70 hours of observing time, using four of the largest ground-based telescopes to estimate their distances. These were the Atacama Large Millimetre Array (Alma), the Very Large Telescope (VLT) and the Gemini South Telescope - all located in Chile - as well as the twin Keck telescopes in Hawaii.

These measurements enabled the team to confirm that they were observing these galaxies when the Universe was 550 million years old.

Knowing the age of the galaxies and when they existed enabled the team to calculate when the first stars were born.

Similar estimates have been made using just single galaxies, but this is the first meaningful estimate based on a representative group of them.

Follow Pallab on Twitter.



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Oct 9, 2004
Zhurong rover's sounds are recorded as it wheels out on to the Martian surface



Hall of Fame Member
Oct 26, 2009
'Extreme' white dwarf sets cosmic records for small size, huge mass
Author of the article:Reuters
Will Dunham
Publishing date:Jun 30, 2021 • 7 hours ago • 3 minute read • Join the conversation
A newfound small white dwarf, called ZTF J1901+1458 and located 130 light-years from Earth, that is slightly larger than the size of the moon in diameter but 1.35 times the mass of our sun, making it both the smallest in size and largest in mass of any known white dwarf is seen in an undated illustration.
A newfound small white dwarf, called ZTF J1901+1458 and located 130 light-years from Earth, that is slightly larger than the size of the moon in diameter but 1.35 times the mass of our sun, making it both the smallest in size and largest in mass of any known white dwarf is seen in an undated illustration. PHOTO BY GIUSEPPE PARISI /Handout via REUTERS
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WASHINGTON — In their death throes, roughly 97% of all stars become a smoldering stellar zombie called a white dwarf, one of the densest objects in the cosmos. A newly discovered white dwarf is being hailed as the most “extreme” one of these on record, cramming a frightful amount of mass into a surprisingly small package.


Article content
Scientists said on Wednesday this highly magnetized and rapidly rotating white dwarf is 35% more massive than our sun yet boasts a petite diameter only a bit larger than Earth’s moon. That means it has the greatest mass and, counterintuitively, littlest size of any known white dwarf, owing to its tremendous density.

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Only two other types of objects – black holes and neutron stars – are more compact than white dwarfs.

The way this white dwarf, named ZTF J1901+1458, was born also is unusual. It apparently is the product of a binary star system in which two stars orbit each other. These two stars separately evolved into white dwarfs at the end of their life cycles, then spiraled toward one another and merged into a single entity.


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With even a smidgen more combined mass, this merger would have resulted in an immense stellar explosion called a supernova, said Caltech astrophysicist Ilaria Caiazzo, lead author of the study published in the journal Nature. It still might explode at some point in the future, Caiazzo added.

“This white dwarf is really extreme,” Caiazzo said. “We found an object that is really at the limit of how small and heavy a white dwarf could be.”

It is located relatively nearby in our Milky Way galaxy, about 130 light years from Earth. A light year is the distance light travels in a year – about 5.9 trillion miles (9.5 trillion km).

The white dwarf is actually shrinking very gradually, becoming ever more dense. If it does not explode, that could lead to a core collapse transforming it into a neutron star, another type of stellar remnant about the size of a city, typically formed after certain very massive stars go supernova. This would be a previously unrecognized path to neutron star formation.


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The white dwarf was spotted by astrophysicist and study co-author Kevin Burdge from Caltech’s Palomar Observatory.

“White dwarfs are the most common form of stellar remnant,” said Burdge, who worked on the study at Caltech and is headed to MIT. “So it’s stunning to see the most extreme outliers among them.”

Its diameter of roughly 2,670 miles (4,300 km) – approximately the distance from Boston to Los Angeles or London to Tehran – slightly exceeds the moon’s diameter of about 2,160 miles (3,475 km).

While our sun rotates around its axis once every 27 days, this white dwarf does so every seven minutes. Its magnetic field is about a billion times stronger than Earth’s.

Stars with up to eight times the mass of our sun are thought to be destined to end up as a white dwarf. Such stars eventually burn up all of the hydrogen they use as fuel through nuclear fusion. At this point, gravity causes them to collapse and blow off their outer layers in a ‘red giant’ stage, eventually leaving a dense core that is a white dwarf.

White dwarfs initially have high temperatures but gradually cool over time, lacking any new energy source. In roughly 5 billion years, our sun is expected to become a red giant and later a white dwarf.


Hall of Fame Member
Oct 9, 2004
I've just been out to put a bin out. It's just gone 1am. I saw a very bright light in the sky to the south east. A massive bright white light fairly low down. It's Saturn. Check it out for yourselves.


Hall of Fame Member
Oct 9, 2004
97% of all the stars in our galaxy will eventually become white dwarves - including the Sun. In turn, white dwarves will eventually become black dwarves. However, as it takes longer than the current age of the Universe to form, no black dwarf yet exists. The Sun will become a black dwarf around a quadrillion years from now.



Hall of Fame Member
Oct 9, 2004

Meet quasar 3C 273, one of the brightest known objects in the Universe. It is 2.5 billion light years away and is 4 TRILLION times brighter than the Sun. If it was 33 light years away from us - the same distance as the star Pollux - it would appear as bright as the Sun.