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A civilization could colonize entire galaxy + Betelgeuse’s dimming finally explained

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Aliens wouldn't need warp drives to take over an entire galaxy, simulation suggests

EXCERPTS: A new computer simulation shows that a technologically advanced civilization, even when using slow ships, can still colonize an entire galaxy in a modest amount of time. The finding presents a possible model for interstellar migration and a sharpened sense of where we might find alien intelligence.

[...] Things start off slow in the simulation, but the civilization’s rate of spread really picks up once the power of exponential growth kicks in. But that’s only part of the story; the expansion rate is heavily influenced by the increased density of stars near the galactic center and a patient policy, in which the settlers wait for the stars to come to them, a result of the galaxy spinning on its axis.

The whole process, in which the entire inner galaxy is settled, takes one billion years. That sounds like a long time, but it’s only somewhere between 7% and 9% the total age of the Milky Way galaxy.

Another neat aspect of the video is that it shows a civilization transitioning from Kardashev II status—in which it harnesses the power of entire star systems—to a full-blown Kardashev III civilization, which has tapped into the energy output of the entire galaxy (more about the Kardashev scale here).

That a civilization might want to embark on such an ambitious enterprise might seem implausible, but it’s important to remember Steven J. Dick’s Intelligence Principle, which states that the “maintenance, improvement and perpetuation of knowledge and intelligence is the central driving force of cultural evolution, and that to the extent intelligence can be improved, it will be improved,” as the science historian wrote in his 2003 paper, “Cultural Evolution, the Postbiological Universe and SETI.” Our civilization keeps pushing the envelope of what’s possible, and we have no reason to believe this urge will cease any time soon. Hence the assumption that advanced civilizations will eventually seek to occupy every corner of the galaxy and set up camp around precious energy sources, namely stars.

My personal hero, the late Carl Sagan, thought it possible that alien civilizations might spawn colonization waves, but he argued that it would take an inordinate amount of time for a civilization to reach Kardashev III status, if ever. The new paper, however, imagines the transition as happening far faster than previously assumed, even under some unreasonably conservative assumptions... (MORE - details)

Betelgeuse’s great dimming has a great explanation

RELEASE: When Betelgeuse, a bright orange star in the constellation of Orion, became visibly darker in late 2019 and early 2020, the astronomy community was puzzled. A team of astronomers have now published new images of the star’s surface, taken using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), that clearly show how its brightness changed. The new research reveals that the star was partially concealed by a cloud of dust, a discovery that solves the mystery of the “Great Dimming” of Betelgeuse.

Betelgeuse’s dip in brightness — a change noticeable even to the naked eye — led Miguel Montargès and his team to point ESO’s VLT towards the star in late 2019. An image from December 2019, when compared to an earlier image taken in January of the same year, showed that the stellar surface was significantly darker, especially in the southern region. But the astronomers weren’t sure why.

The team continued observing the star during its Great Dimming, capturing two other never-before-seen images in January 2020 and March 2020. By April 2020, the star had returned to its normal brightness.

“For once, we were seeing the appearance of a star changing in real time on a scale of weeks,” says Montargès, from the Observatoire de Paris, France, and KU Leuven, Belgium. The images now published are the only ones we have that show Betelgeuse’s surface changing in brightness over time.

In their new study, published today in Nature, the team revealed that the mysterious dimming was caused by a dusty veil shading the star, which in turn was the result of a drop in temperature on Betelgeuse’s stellar surface.

Betelgeuse’s surface regularly changes as giant bubbles of gas move, shrink and swell within the star. The team concludes that some time before the Great Dimming, the star ejected a large gas bubble that moved away from it. When a patch of the surface cooled down shortly after, that temperature decrease was enough for the gas to condense into solid dust.

“We have directly witnessed the formation of so-called stardust,” says Montargès, whose study provides evidence that dust formation can occur very quickly and close to a star’s surface. “The dust expelled from cool evolved stars, such as the ejection we’ve just witnessed, could go on to become the building blocks of terrestrial planets and life,” adds Emily Cannon, from KU Leuven, who was also involved in the study.

Rather than just the result of a dusty outburst, there was some speculation online that Betelgeuse’s drop in brightness could signal its imminent death in a spectacular supernova explosion. A supernova hasn’t been observed in our galaxy since the 17th century, so present-day astronomers aren’t entirely sure what to expect from a star in the lead-up to such an event. However, this new research confirms that Betelgeuse's Great Dimming was not an early sign that the star was heading towards its dramatic fate.

Witnessing the dimming of such a recognisable star was exciting for professional and amateur astronomers alike, as summed up by Cannon: “Looking up at the stars at night, these tiny, twinkling dots of light seem perpetual. The dimming of Betelgeuse breaks this illusion.”

The team used the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on ESO’s VLT to directly image the surface of Betelgeuse, alongside data from the GRAVITY instrument on ESO’s Very Large Telescope Interferometer (VLTI), to monitor the star throughout the dimming. The telescopes, located at ESO’s Paranal Observatory in Chile’s Atacama Desert, were a “vital diagnostic tool in uncovering the cause of this dimming event,” says Cannon. “We were able to observe the star not just as a point but could resolve the details of its surface and monitor it throughout the event,” Montargès adds.

Montargès and Cannon are looking forward to what the future of astronomy, in particular what ESO’s Extremely Large Telescope (ELT), will bring to their study of Betelgeuse, a red supergiant star. “With the ability to reach unparalleled spatial resolutions, the ELT will enable us to directly image Betelgeuse in remarkable detail,” says Cannon. “It will also significantly expand the sample of red supergiants for which we can resolve the surface through direct imaging, further helping us to unravel the mysteries behind the winds of these massive stars.”

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