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Giant star spots likely cause of Betelgeuse dimming – Phys.org

Betelgeuse—a giant with blemishes
Red Supergiant: An artist’s impression of Betelgeuse. Its surface is covered by large star spots, which reduce its brightness. During their pulsations, such stars regularly release gas into their surroundings, which condenses into dust. Credit: MPIA graphics department

Betelgeuse, the bright star in the constellation of Orion, has been fascinating astronomers in the recent months because of its unusually strong decline in brightness. Scientists have been discussing a number of scenarios trying to explain its behavior. Now a team led by Thavisha Dharmawardena of the Max Planck Institute for Astronomy have shown that most likely unusually large star spots on the surface of Betelgeuse have caused the dimming. Their results rule out the previous conjecture that it was dust, recently ejected by Betelgeuse, which obscured the star.

Red giant stars like Betelgeuse undergo frequent brightness variations. However, the striking drop in Betelgeuse’s luminosity to about 40% of its normal value between October 2019 and April 2020 came as a surprise to astronomers. Scientists have developed various scenarios to explain this change in the brightness of the star, which is visible to the naked eye and almost 500 away. Some astronomers even speculated about an imminent supernova. An international team of astronomers led by Thavisha Dharmawardena from the Max Planck Institute for Astronomy in Heidelberg have now demonstrated that in the photosphere, i.e. the luminous surface of the star, caused the brightness to drop. The most plausible source for such temperature changes are gigantic cool star spots, similar to sunspots, which, however, cover 50 to 70% of the star’s surface.

“Towards the end of their lives, stars become red giants,” Dharmawardena explains. “As their fuel supply runs out, the processes change by which the stars release energy.” As a result, they bloat, become unstable and pulsate with periods of hundreds or even thousands of days, which we see as a fluctuation in brightness. Betelgeuse is a so-called Red Supergiant, a star which, compared to our sun, is about 20 more massive and roughly 1000 times larger. If placed in the center of the solar system, it would almost reach the orbit of Jupiter.

Because of its size, the gravitational pull on the surface of the star is less than on a star of the same mass but with a smaller radius. Therefore, pulsations can eject the outer layers of such a star relatively easily. The released gas cools down and develops into compounds that astronomers call dust. This is why are an important source of heavy elements in the Universe, from which planets and living organisms eventually evolve. Astronomers have previously considered the production of light absorbing dust as the most likely cause of the steep decline in brightness.

Betelgeuse—a giant with blemishes
Light and dark: These high-resolution images of Betelgeuse show the distribution of brightness in visible light on its surface before and during its darkening. Due to the asymmetry, the authors conclude that there are huge stars pots. The images were taken by the SPHERE camera of the European Southern Observatory (ESO). Credit: ESO / M. Montargès et al.

To test this hypothesis, Thavisha Dharmawardena and her collaborators evaluated new and archival data from the Atacama Pathfinder Experiment (APEX) and the James Clerk Maxwell telescope (JCMT). These telescopes measure radiation from the spectral range of submillimeter waves (terahertz radiation), whose wavelength is a thousand times greater than that of visible light. Invisible to the eye, astronomers have been using them for some time to study interstellar dust. Cool dust in particular glows at these wavelengths.

“What surprised us was that Betelgeuse turned 20% darker even in the submillimeter wave range,” reports Steve Mairs from the East Asian Observatory, who collaborated on the study. Experience shows that such behavior is not compatible with the presence of dust. For a more precise evaluation, she and her collaborators calculated what influence dust would have on measurements in this spectral range. It turned out that indeed a reduction in brightness in the sub-millimeter range cannot be attributed to an increase in dust production. Instead, the star itself must have caused the brightness change the astronomers measured.

Physical laws tell us that the luminosity of a star depends on its diameter and especially on its surface temperature. If only the size of the star decreases, the luminosity diminishes equally in all wavelengths. However, temperature changes affect the radiation emitted along the electromagnetic spectrum differently. According to the scientists, the measured darkening in and submillimeter waves is therefore evidence of a reduction in the mean surface temperature of Betelgeuse, which they quantify at 200 K (or 200 °C).

“However, an asymmetric temperature distribution is more likely,” explains co-author Peter Scicluna from the European Southern Observatory (ESO). “Corresponding high-resolution images of Betelgeuse from December 2019 show areas of varying brightness. Together with our result, this is a clear indication of huge star spots covering between 50 and 70% of the visible surface and having a lower temperature than the brighter photosphere.” Star spots are common in giant stars, but not on this scale. Not much is known about their lifetimes. However, theoretical model calculations seem to be compatible with the duration of Betelgeuse’s dip in brightness.

We know from the sun that the amount of spots increases and decreases in an 11-year cycle. Whether giant have a similar mechanism is uncertain. An indication for this could be the previous brightness minimum, which was also much more pronounced than those in previous years. “Observations in the coming years will tell us whether the sharp decrease in Betelgeuse’s is related to a spot cycle. In any case, Betelgeuse will remain an exciting object for future studies,” Dharmawardena concludes.



More information:
Thavisha E. Dharmawardena et al. Betelgeuse Fainter in the Submillimeter Too: An Analysis of JCMT and APEX Monitoring during the Recent Optical Minimum, The Astrophysical Journal (2020). DOI: 10.3847/2041-8213/ab9ca6

Citation:
Giant star spots likely cause of Betelgeuse dimming (2020, June 29)
retrieved 29 June 2020
from https://phys.org/news/2020-06-giant-star-betelgeuse-dimming.html

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Coronavirus spots

Coronavirus hot spots see rare good news as the nation debates over reopening – CNN

(CNN)An inflammatory illness recently observed in dozens of New York children — one that state health officials say may be linked to Covid-19 — has killed a teenager and two children under 8 years old, state officials said Saturday.

The state is trying to determine whether the novel coronavirus indeed poses a threat to children that hadn’t previously been recognized, and is working with federal officials on how to explain what other states’ hospitals should be looking for, Gov. Andrew Cuomo said.
“We were laboring under the impression young people were not affected by Covid-19. … We’re not so sure that that is the fact anymore,” Cuomo told reporters Saturday.
State officials had warned earlier this week that dozens of children in the state had been hospitalized with a condition doctors described as “pediatric multisystem inflammatory syndrome,” and that it could be linked to Covid-19.
The children had fever and symptoms similar to toxic shock syndrome and Kawasaki disease, the state had said. Kawasaki disease causes inflammation in the walls of blood vessels, including those that supply blood to the heart, which in rare cases can lead to deadly limitations in blood flow.
The state has said many of the children tested positive for Covid-19 or had Covid-19 antibodies. But they didn’t necessarily present with typical symptoms for the coronavirus disease, such as respiratory distress, Cuomo said.
The state now knows of 73 children with the syndrome, and three of them have died, Cuomo said.
His office said they were: A 5-year-old boy who died Thursday in New York City; a 7-year-old boy in Westchester County; and a teenager in Suffolk County. No names were released.
Researchers still don’t know whether coronavirus caused the syndrome. But this is under investigation, Cuomo said.
“We still have a lot to learn about this virus,” he said.
Similar reports of this syndrome in children have appeared elsewhere: In Seattle; at Stanford Children’s Hospital in California; and in the United Kingdom, Italy and Spain.

Some coronavirus hot spots see rare good news as the nation debates over reopening

There have been glimmers of hope in some coronavirus hot spots in the United States amid frustration as states continue reopening.
In New York, the numbers of new daily cases, hospitalizations and intubations are declining, Cuomo said Saturday.
Numbers appear better in other parts of the US, too. Hawaii on Friday reported no confirmed cases of coronavirus for the first time since March 13. Meanwhile, Friday was the second day in a row that hard-hit New Orleans in Louisiana reported no new coronavirus deaths.
Those bright spots come as swaths of the country continue to disagree on how to move forward with battling the deadly virus.
By Sunday, at least 47 states will have eased restrictions meant to slow the spread of the virus. These states are allowing some combination of businesses, services or parks to reopen or restart, often with caveats for spacing and sanitation.
Still, more than two-thirds of Americans worry that their states are reopening too quickly, according to a new poll from the Pew Research Center. Yet protesters have taken to the streets in some states, demanding that businesses get people back to work quicker.
In South Dakota, state officials and two Sioux tribes are at odds over checkpoints that the tribes set up on state and US highways to keep the virus from tribal lands. Gov. Kristi Noem on Friday gave the tribes 48 hours to remove the checkpoints or risk legal action.
At least five states — California, Nevada, North Dakota, Maryland and Rhode Island — are easing some restrictions this weekend. In California, retailers were allowed to offer curbside pickup Friday, and Los Angeles on Saturday will reopen its trails, parks and golf courses.
And Saturday is expected to offer the country’s first major sports event since the virus lockdowns began in March. UFC 249 is scheduled to kick off Saturday evening in Jacksonville, Florida — viewable by livestream and TV, with no spectators at the venue — though one preliminary-card fighter has withdrawn after testing positive for the virus.
Some health experts have warned that states are not ready to relax restrictions, saying they’ve not met all federal guidelines, such as having aggressive testing.
These experts say reopening now could lead to alarming spikes in the number of infections and that because it takes time for symptoms to show, it could be weeks before the US sees the spikes.

Infections from the White House to prisons

As states continue to navigate the reopening process, the White House is coping with at least two cases of the virus among its staff members.
One of President Donald Trump’s personal valets, a member of the US Navy, tested positive for the coronavirus, CNN learned Thursday. Valets assist the President and first family and are responsible for the President’s food and beverages.
Vice President Mike Pence’s press secretary, Katie Miller, tested positive Friday for the virus, Trump confirmed. Miller has not come into contact with Trump, but she had been in contact with Pence, the President said.
The President and Vice President have recently tested negative, deputy White House press secretary Hogan Gidley said.
The head of the Food and Drug Administration, meanwhile, will self-quarantine for 14 days after coming in contact with a person who tested positive for the virus, an FDA spokesman said Friday. The FDA did not name the person with whom the FDA chief, Dr. Stephen Hahn, came into contact.
Elsewhere, federal and state prisons have had thousands of inmates test positive for the virus. The facilities that often are limited in the abilities to socially distance have been the site of some state’s biggest outbreaks.
In Arkansas, more than 1,000 inmates have tested positive — with 876 from a single correctional facility, according to Dr. Nate Smith, the Director of the Arkansas Department of Health. For Ohio, 20% of the state’s infections are attributed to people behind bars.
Throughout the pandemic’s hold on the US, nursing homes also have been especially vulnerable. The large populations in close quarters as well as the virus’s severity on older adults has led to large numbers of infections.

Tempers flare over masks and business restrictions

Tempers have flared in some parts of the country over business closures and over some local or state governments’ guidelines about wearing masks in public places.
In Alabama, police say a woman became disorderly Tuesday at a Walmart in Birmingham after a worker asked her to put on a mask before entering the store. Video shows an off-duty officer lifting the woman up and dropping her to the ground while trying to detain her; police say she’s been charged with disorderly conduct and other counts.
In Michigan, a Family Dollar security guard was shot dead last week after he told a woman to wear a face mask, officials said. Police also arrested a man who allegedly wiped his nose on the sleeve of a Dollar Tree employee who asked him to wear a mask.
Protesters flocked the Michigan Capitol in recent days, demanding an end to the state of emergency in place through May 28. But Gov. Gretchen Whitmer also relaxed restrictions so some businesses can reopen and the public can participate in outdoor activities like golf and motorized boating.
In Florida’s Miami-Dade County, a bus driver says that after she asked a coughing passenger to wear a mask, that person spat on her and fled. In Miami Beach, a man shouted “this is a false flag, a fake pandemic” in a grocery store during a profanity-laced tirade this week as a code compliance officer told him he needed a mask to enter.
The city of Stillwater, Oklahoma, revoked an order requiring residents to wear face coverings inside buildings after workers received threats.

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