WHAT JUST HAPPENED TO BETELGEUSE?

Jan 27, 2020
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You've heard of a CME, a "coronal mass ejection." They happen all the time. A piece of the sun's tenuous outer atmosphere (corona) blows off and sometimes hits Earth. Something far more terrible just happened to Betegeuse. The red giant star produced an SME, or "surface mass ejection."

SME_strip.jpeg

Above: An artist's concept of an SME on Betelgeuse. Credit: Elizabeth Wheatley (STScI)

NASA astronomers believe that in 2019 a colossal piece of Betelgeuse's surface blew off the star. The mass of the SME was 400 billion times greater than a CME or several times the mass of Earth's Moon. Data from multiple telescopes, especially Hubble, suggest that a convective plume more than a million miles across bubbled up from deep inside the star, producing shocks and pulsations that blasted a chunk off the surface.

"We've never before seen such a huge mass ejection from the surface of a star," says Andrea Dupree of the Harvard-Smithsonian Center for Astrophysics, who is leading the study. "Something is going on that we don't completely understand."

After it left the star, the SME cooled, forming a dark cloud that famously dimmed Betelgeuse in 2019 and 2020. Even casual sky watchers could look up and see the change. Some astronomers worried that the dimming foreshadowed a supernova explosion. The realization that an SME is responsible has at least temporarily calmed those fears.

betelgeuse.jpeg
Above: A Hubble image of Betelgeuse located in the shoulder of Orion.

Betelgeuse's brightness has since returned to normal, but something strange is still going on. Astronomers have long known that Betelgeuse is a variable star with a 430-day period. Its metronome-like change in brightness has been observed for more than 200 years. As Betelgeuse recovers, however, those pulsations are no longer regular: See the data. Spectra taken by Hubble and the Tillinghast telescope in Arizona imply that years later the surface of Betelgeuse is still bouncing like a plate of gelatin dessert--a testament to the ferocity of the blowout.

Betelgeuse, a red giant star*, is so large that if it replaced the sun at the center of our solar system, its atmosphere would extend past Jupiter. Dupree used Hubble to resolve hot spots on the star's surface in 1996. This was the first direct image of a star other than the sun.

What's happening now "is a totally new phenomenon that we can observe directly and resolve surface details with Hubble," says Dupree. "We're watching stellar evolution in real time."

See: https://spaceweather.com

* Red giant star - is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. Its outer atmosphere is inflated and tenuous making its radius several times larger than that of our Sun, and the surface temperature is usually around 5,000 K.

  • A red giant star’s appearance is usually from yellow-orange to red, including the spectral types K and M, but also S class stars and carbon stars.
  • A red giant star is a dying star in the last stages of its stellar evolution.
  • Red giant stars usually result from low and intermediate-mass main-sequence stars of around 0.5 to 5 solar masses.
  • Red giant stars differ in a way by which they generate energy.
  • Most of the well-known bright stars are red giants, due to their luminosity and because they are moderately common.
  • Red giant stars no longer perform nuclear fusion between helium and hydrogen in their cores and thus they heat up and expand several times their previous size.
  • All stars die when they burn up all their fuel and there is no more pressure to keep gravity pushing towards their centers.
  • Red giant stars are between 100 to 1.000 times more luminous than our Sun.
  • Most red giant stars live up to around 0.1 to 2 billion years.
  • Red giant stars are much smaller and much less massive than red supergiant stars.
  • Some famous red giant stars are Aldebaran and Arcturus.
  • Our own star, the Sun, will eventually become a red giant star and expand several times its current diameter.
  • One of the biggest red giants ever discovered is VY Canis Majoris, being around 1,400 times bigger than our Sun.
  • Some red giants have planets orbiting around them. It is theorized that red giants can have a stable habitable zone, allowing life to probably develop on planets.
  • The Earth will eventually be consumed by a red giant, our own Jolly Old Mr Sun.
The majority of stars in the universe are main-sequence**stars – they are stars that still convert hydrogen into helium through nuclear fusion. Main-sequence stars have a mass between a third to eight times that of the Sun, and they eventually burn through their hydrogen supplies.

A red giant star is formed when a star, like our Sun, burns all of its hydrogen and helium supplies. This process can take up to 10 billion years.



When a star becomes a red giant, it will start to expand and become less dense. It will then start burning helium to carbon for a couple of million of years until, eventually, the helium runs out.

When helium runs out, the star will not be dense enough to form other heavy elements like iron, thus the fusion process will stop, and the star will collapse on its core due to inward acting gravity.

This happens because there is no longer any fusion energy to stabilize gravity. Red giant may eventually become white dwarfs, a cool and extremely dense star, with its size being shrunk several times, to that of a planet even.

A red giant star can reach sizes of about 100 million to 1 billion kilometers / 62 million to 621 million miles in diameter, or 100 to 1,000 times the size of our Sun.

Since a red giant star’s energy spreads across a larger area, its surface temperatures are cooler, reaching only 2,200 to 3,200 degrees Celsius / 4,000 to 5,800 degrees Fahrenheit, a little over half as hot as our Sun.

Red-Giant-Star.png

Because of this change in temperature, the star begins to shine in the redder part of the spectrum, leading to the name red giant, though they are often more orange in appearance.

Red giants stars remain in this stage from a few thousand to 1 billion years. They eventually run out of helium in their cores and thus fusion stops.

This causes the star to shrink until a new helium shell reaches its core. When the helium ignites, the outer layers of the star are blown off in huge clouds of gas and dust known as planetary nebulae. These shells are much larger and fainter than their parent stars.

Red giants evolve out of main-sequence stars that have masses in the range from around 0.3 solar masses to around 8 solar masses. Stars initially form from collapsing molecular clouds in the interstellar medium.

These clouds contain hydrogen and helium, with trace amounts of metals, and all of these elements are uniformly mixed throughout the star.



The star reaches the main sequence when the core reaches a temperature high enough to begin fusing hydrogen and establishes hydrostatic equilibrium.

Over a star’s main sequence life, it slowly converts hydrogen in the core to helium. A star’s main sequence life ends when nearly all its hydrogen supplies in the core have been fused.

When the hydrogen supplies are exhausted, nuclear reactions can no longer continue and thus the core begins to contract due to its own gravity.

This brings additional hydrogen into a zone where the temperature and pressure are sufficient to cause fusion to resume in a shell around the core.

The hydrogen-burning shell results in a situation that has been described as the mirror principle, when the core within the shell contracts, the layers of the star outside the shell must expand.

The evolutionary path the star takes as it moves along the red-giant phase depends solely on its mass. For example, the Sun and stars of less than 2 solar masses, the core will become dense enough that electron degeneracy pressure will prevent it from collapsing further.

Sun_red_giant.png

It varies slightly in brightness between magnitudes 0.75 and 0.95 – however, this cannot be observed with the naked eye.

Arcturus is a red giant star located at around 36.7 light-years away from the Sun. It is the brightest star in the constellation of Boötes. It is also the fourth brightest star in the night sky, yet the brightest in the northern hemisphere.


Another example of a red giant is Gacrux. It is the third brightest star in the Southern Cross asterism. All of its star neighbors are blue, thus Gacrux stands out with its reddish color. It is situated at 88.6 light-years away from us.

Red giant stars live for many years, and we don’t have to worry about them. However, in approximately 5 billion years from now, a red giant will emerge quite close to us.

Our Sun will actually become a red giant star. When this will happen, the Sun will expand its outer layers and consume Mercury, Venus, and eventually Earth.
  • When the Sun will become a red giant, its radius will increase to nearly 100 times its present size, and its temperatures will drop as low as 3,000 K.
  • In a red giant, a huge, cool, and low-density hydrogen envelope encloses a small, hot, high-density helium core – with a density of about 1,000 tons / m3.
  • Red giants are several times more luminous than our Sun due to their great size.
  • Some red giants can become so large, that if we were to replace our Sun with one of them, they could reach the orbits of Mars and Jupiter, and even beyond.
See: https://nineplanets.org/red-giant-star/

** Stellar main sequence - Hertzsprung-Russell diagram:

main sequence.jpeg
Ron Miller / Stocktrek Images / Getty Images

Generally, the H-R diagram is a "plot" of temperature vs. luminosity. Think of "luminosity" as a way to define the brightness of an object. Temperature is something we're all familiar with, generally as the heat of an object. It helps define something called a star's spectral class, which astronomers also figure out by studying the wavelengths of light that come from the star. So, in a standard H-R diagram, spectral classes are labeled from hottest to coolest stars, with the letters O, B, A, F, G, K, M (and out to L, N, and R). Those classes also represent specific colors. In some H-R diagrams, the letters are arranged across the top line of the chart. Hot blue-white stars lie to the left and the cooler ones tend to be more toward the right side of the chart.

The basic H-R diagram is labeled as the one shown here. The nearly diagonal line is called the main sequence. Nearly 90 percent of the stars in the universe exist along that line at one time in their lives. They do this while they are still fusing hydrogen to helium in their cores. Eventually, they run out of hydrogen and start to fuse helium. That's when they evolve to become giants and supergiants. On the chart, such "advanced" stars end up in the upper right corner. Stars like the Sun may take this path, and then ultimately shrink down to become white dwarfs, which appear in the lower-left part of the chart.

The H-R diagram was developed in 1910 by the astronomers Ejnar Hertzsprung and Henry Norris Russell. Both men were working with spectra of stars — that is, they were studying the light from stars by using spectrographs. Those instruments break down the light into its component wavelengths. The way the stellar wavelengths appear gives clues to the chemical elements in the star. They can also reveal information about its temperature, motion through space, and its magnetic field strength. By plotting the stars on the H-R diagram according to their temperatures, spectral classes, and luminosity, astronomers can classify stars into their different types.

Today, there are different versions of the chart, depending on what specific characteristics astronomers want to chart. Each chart has a similar layout, with the brightest stars stretching up toward the top and veering off to the top left, and a few in the lower corners.

The H-R diagram uses terms that are familiar to all astronomers, so it's worth learning the "language" of the chart. Most observers have probably heard the term "magnitude" when applied to stars. It's a measure of a star's brightness. However, a star might appear bright for a couple of reasons:
  • It could be fairly close and thus look brighter than one farther away
  • It could be brighter because it's hotter.
For the H-R diagram, astronomers are mainly interested in a star's "intrinsic" brightness — that is, its brightness due to how hot it actually is. That's why luminosity (mentioned earlier) is plotted along the y-axis. The more massive the star is, the more luminous it is. That's why the hottest, brightest stars are plotted among the giants and supergiants in the H-R Diagram.

Temperature and/or spectral class are, as mentioned above, derived by looking at the star's light very carefully. Hidden within its wavelengths are clues about the elements that are in the star. Hydrogen is the most common element, as shown by the work of astronomer Cecelia Payne-Gaposchkin in the early 1900s. Hydrogen is fused to make helium in the core, so that's why astronomers see helium in a star's spectrum, too. The spectral class is very closely related to a star's temperature, which is why the brightest stars are in classes O and B. The coolest stars are in classes K and M. The very coolest objects are also dim and small, and even include brown dwarfs.

One thing to keep in mind is that the H-R diagram can show us what stellar type a star can become, but it doesn't necessarily predict any changes in a star. That's why we have astrophysics — which applies the laws of physics to the lives of the stars.

See: https://www.thoughtco.com/hertzsprung-russell-diagram-4134689

Betelgeuse is currently in the red supergiant phase, a typical evolutionary stage of stars with masses between 10 and 40 solar masses, characterized by an enormous expansion of the stellar envelope in response to changes in energy generation processes that have begun exiting the main sequence. There is a fairly broad consensus among astronomers that Betelgeuse is now ascending the supergiant branch for the first time. It means that the production of energy inside it is supported by the nuclear fusion of helium in carbon and oxygen, which takes place in the core of the star, and hydrogen in helium, which occurs in a shell outside the core.

As regarding stellar classification, Betelgeuse has been cataloged, starting from the introduction of the Morgan-Keenan system, with the spectral types M1-M2Ia-Iab. Variability in type attribution reflects the intrinsic variability of the star and its spectrum. The general characteristics are, in any case, those of a luminous red supergiant.

An element of considerable uncertainty concerns the mass. Despite many searches and some attempted identifications, the existence of a binary companion of the supergiant has never been confirmed. So, to derive its mass from orbital parameters by Newtonian gravity formulas is impossible. Therefore, the only way to estimate Betelgeuse’s mass is to use appropriate stellar evolution models, to find the evolutionary track that best suits the observable characteristics of the star.

Precisely using stellar evolution models, Michelle M. Dolan and others had calculated in 2008 a mass equal to 16 ± 2 solar masses. The same Dolan, together with other authors, published in 2016 a new study on Betelgeuse in The Astrophysical Journal. In it, along with a new estimate of the mass, a complete identity card of the star was drawn, putting together all the possible physical parameters, both those derived directly from observation and those derived from stellar evolution models. Dolan and colleagues estimated an initial mass, at the beginning of the main sequence, of 20 solar masses with a margin of uncertainty of +5 and −3 solar masses.

Someday a supernova explosion will disintegrate Betelgeuse, generating an immense cloud of debris that will expand at a very high speed. Only a tiny, ultra-dense collapsed part of the core will remain of the progenitor star: a neutron star of about 1.5 solar masses. The actual brightness of the event is quadrillions of times higher than that currently seen.

Below is a list of the main parameters of Betelgeuse defined in that study:
  • distance: 197 ± 45 parsec;
  • radial velocity: 21.91 ± 0.51 km/s;
  • diameter: 887 ± 203 solar diameters, equal to (1.23 ± 0.28) × 10⁹ km;
  • luminosity: 125,900 solar luminosities (4.845 × 10³¹ watts) [2];
  • effective temperature: 3,500 ± 200 K;
  • rotational velocity: 5 km/s (inclination angle: 20 degrees);
  • rotational period: 8.4 years;
  • composition: 70% hydrogen, 28% helium, 2.4% other elements;
  • current mass: 19.4 solar masses (3.86 × 10³¹ kg);
  • mass loss: (2 ± 1)×10⁻⁶ solar masses/year;
  • surface gravity: 0.3 cm/s²;
  • age: 8−8.5 million years;
  • Expected demise: Type II-P supernova.
See: https://medium.com/amazing-science/all-about-betelgeuse-live-fast-die-young-a524828c4a69

I always find it fascinating to follow stars like our Sun as they move along the main sequence and then end their stellar lives as red giants. Betelgeuse is now ascending the supergiant branch for the first time and has made this progression along the main sequence and is now a red super giant, indicating that the initial state of Betelgeuse was far more massive than the Sun, some 10-40 solar masses. Betelgeuse will end its life as a Type II supernova***.
Hartmann352

*** Type II supernovae: are associated with the core collapse of a massive star together with a shock-driven expansion of a luminous shell which leaves behind a rapidly rotating neutron star or, if the core has mass of >2–3 solar masses, a black hole.

The typical signal from such an explosion is broadband and peaked at around 1 kHz. Detection of such a signal has been the goal of detector development over the last three decades. However, we still know little about the efficiency with which this process produces gravitational waves. For example, an exactly spherical collapse will not produce any gravitational radiation at all. The key issue is the kinetic energy of the nonspherical motions since the gravitational wave amplitude is proportional to this.

After 30 years of theoretical and numerical attempts to simulate gravitational collapse, there is still no great progress in understanding the efficiency of this process in producing gravitational waves. For a conservative estimate of the energy in nonspherical motions during the collapse, relation leads to events of an amplitude detectable in our galaxy, even by bar detectors. The next generation of laser interferometers would be able to detect such signals from the Virgo cluster at a rate of a few events per month.

The main source of nonsphericity during the collapse is the angular momentum. During the contraction phase, the angular momentum is conserved and the star spins up to rotational periods of the order of 1 msec. In this case, a number of consequent processes with large luminosity might take place in this newly born neutron star. A number of instabilities, such as the so-called bar mode instability and the r mode instability, may occur which radiate copious amounts of gravitational radiation immediately after the initial burst. Gravitational wave signals from these rotationally induced stellar instabilities are detectable from sources in our galaxy and are marginally detectable if the event takes place in the nearby cluster of about 2500 galaxies, the Virgo cluster, 15 Mpc away from the earth. Additionally, there will be weaker but extremely useful signals due to subsequent oscillations of the neutron star; f, p, and w modes are some of the main patterns of oscillations (normal modes) of the neutron star that observers might search for. These modes have been studied in detail, and once detected in the signal, they would provide a sensitive probe of the neutron star structure and its supranuclear equation of state. Detectors with high sensitivity in the kilohertz band will be needed in order to fully develop this so-called gravitational wave asteroseismology.

If the collapsing central core is unable to drive off its surrounding envelope, then the collapse continues and finally a black hole forms. In this case the instabilities and oscillations discussed above are absent and the newly formed black hole radiates away within a few milliseconds any deviations from axisymmetry and ends up as a rotating or Kerr black hole. The characteristic oscillations of black holes (normal modes) are well studied, and this unique ringing down of a black hole could be used as a direct probe of their existence. The frequency of the signal is inversely proportional to the black hole mass.

For example, it was stated earlier that a 100-solar-mass black hole will oscillate at a frequency of ∼100 Hz (an ideal source for LIGO), while a supermassive one with mass 107 solar masses, which might be excited by an infalling star, will ring down at a frequency of 10−3 Hz (an ideal source for LISA). The analysis of such a signal should reveal directly the two parameters that characterize any (uncharged) black hole, namely its mass and angular momentum.

See: https://www.sciencedirect.com/topics/physics-and-astronomy/type-ii-supernovae

To better understand the f and p mode oscillations of stars, this paper might be of some interest: https://arxiv.org/abs/2205.02081

An additional paper providing information on stellar oscillations, see: https://cds.cern.ch/record/257653/files/P00020353.pdf
 
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Mar 4, 2020
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It looks spectacular. Too bad we don't have instruments that can capture these events with better resolution and detail. And display the actual images, not an inferred artist's rendition. I wonder what the duration of the ejection was. Minutes, hours or maybe days.

I remember reading about the dimming a few years ago. The various articles and narratives. It was a close by event, given the 550 LY distance, with a galactic diameter of 100,000 LY. So this took place 550 yrs ago. + or - a decade or so.

Maybe WEBB can look a little closer, maybe even detect a trail. How long would it take such a blob to disperse? This burping might be more common or even part of a red star's process. If the burping cycle has a long duration, say a million years or longer, it might be hard to find another. We need lots of twinkle detectors. If we seed the solar system thru-out with antenna elements, and link them together, we might have an aperture the size of our system. That's a large light gathering area. We should be able to detect a very large spectrum. Fill the planetary L points first. Add radar to the elements and scan for flying rocks too.

Too hard to read the whole post with these eyes, maybe in a few weeks.
 
Jan 27, 2020
422
110
1,880
It looks spectacular. Too bad we don't have instruments that can capture these events with better resolution and detail. And display the actual images, not an inferred artist's rendition. I wonder what the duration of the ejection was. Minutes, hours or maybe days.

I remember reading about the dimming a few years ago. The various articles and narratives. It was a close by event, given the 550 LY distance, with a galactic diameter of 100,000 LY. So this took place 550 yrs ago. + or - a decade or so.

Maybe WEBB can look a little closer, maybe even detect a trail. How long would it take such a blob to disperse? This burping might be more common or even part of a red star's process. If the burping cycle has a long duration, say a million years or longer, it might be hard to find another. We need lots of twinkle detectors. If we seed the solar system thru-out with antenna elements, and link them together, we might have an aperture the size of our system. That's a large light gathering area. We should be able to detect a very large spectrum. Fill the planetary L points first. Add radar to the elements and scan for flying rocks too.

Too hard to read the whole post with these eyes, maybe in a few weeks.
Hay
 
Jan 27, 2020
422
110
1,880
Hayseed -

The Webb ST should certainly improve the resolution due to the total size of its mirrors. The JWST is 100x more powerful than the Hubble Space Telescope is.

Here's a shot:

betelgeuse atacama.jpeg
Betelgeuse as seen by ALMA. Credit: ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella

This orange blob shows the nearby star Betelgeuse, as seen by the Atacama Large Millimeter/submillimeter Array (ALMA). This is the first time that ALMA has ever observed the surface of a star and this first attempt has resulted in the highest-resolution image of Betelgeuse available.

Betelgeuses-Dust-Cloud-.jpeg
New observations by the NASA/ESA Hubble Space Telescope suggest that the unexpected dimming of the supergiant star Betelgeuse was most likely caused by an immense amount of hot material that was ejected into space, forming a dust cloud that blocked starlight coming from the star’s surface.

This artist’s impression was generated using an image of Betelgeuse from late 2019 taken with the SPHERE instrument on the European Southern Observatory’s Very Large Telescope. Credit: ESO, ESA/Hubble, M. Kornmesser

Betelgeuse-Atmosphere-.jpeg
This is the first direct image of a star other than the Sun, made with the Hubble Space Telescope in January 2019. Called Alpha Orionis, or Betelgeuse, it is a red supergiant star marking the shoulder of the winter constellation Orion the Hunter.

The Hubble image reveals a huge ultraviolet atmosphere with a mysterious hot spot on the stellar behemoth’s surface. The enormous bright spot, which is many hundreds times the diameter of Sun, is at least 2, 000 Kelvin degrees hotter than the surface of the star. Credit: Andrea Dupree (Harvard-Smithsonian CfA), Ronald Gilliland (STScI), NASA and ES
 

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