The latest in Ph-word: December 2019

No signs from the dark

Deep under the ground of Gran Sasso in Italy lurks XENON1T, an assassin of dark matter hopes. The cold heart of this experiment hides two tons of liquid xenon, whose atoms get kicked out of position by passing dark matter particles, giving flashes of light in the process. Or at least that’s what physicists would hope, but the only things that kicked xenon atoms during the past two years were boring particles, like neutrinos sent by the sun.

XENON1T itself, however, is in top form; hardware upgrades and improved analysis have earned it a position several steps ahead of similar experiments. So, its recent announcement of results from the last couple of years axed various possible “candidates”, hypothesized particles that could be The dark matter, without any signals of discovery emerging from its heartless depths. (Mandatory optimistic disclaimer: The search is not over yet, of course, and optimists like to think that the more candidates we chop the closer we are getting to the real thing.)

News from the pin lights

January might have characteristically clear skies and stars can be admired doing their blinking (wherever the hell there is no photopollution); but last month we had two cases of really blinking stars. One concerns the last several decades, the other is happening now right in front of our eyes, both are unexpected.

By comparing data of the last seven decades, the VASCO project found about a hundred stars in the Milky Way to have serious changes in their brightness during that time. They either lit up, or dimmed down, or fluctuated and even… vanished. Note that this is neither about going through different stages, as stars do during their lifetimes (it’d be slower), nor going supernova (it’d be faster) and it doesn’t look like already known phenomena. One more entry for the mysteries-of-the-universe book, then.

Betelgeuse is one of the brightest stars in the sky, marking the left shoulder of Orion (and, if you know who Zaphod is, it’s also his homeland). Betelgeuse’s light often changes a little due to it being a red supergiant and continuously losing mass. Over the past few weeks, however, its brightness dropped so dramatically that the change is visible even by naked eye!

Such a change has happened before, but it’s been more than a century since it last was so rapid, and the reason it’s attracting attention is that it could signal the beginning of Betelgeuse becoming a supernova. To be honest the chance for this to happen is disappointingly low (but if it happens then it can’t be missed: the supernova will be the brightest object in the night sky for months).

Updates from the nearest star

In the beginning of last year Parker Solar Probe, which had left for our closest star two summers ago, reached the edges of corona and what it saw now got to be revealed to the public. (The corona, despite being the sun’s outer atmosphere, is inexplicably much warmer than its surface and “much” means by a million degrees. So one can say that it’s also the most mysterious part of the sun.) Interesting things are already lurking in the results – like powerful waves in the solar wind with velocity occasionally hitting 500 thousand kilometres per hour – and the general feeling is that this is only the beginning for the Probe.

Incidentally, it seems that last month the new solar 11-year cycle has begun timidly with a few new sunspots darkening the sun’s surface. Now, handfuls of sunspots belonging to both the previous and the new cycles are expected to coexist for an unknown length of time, while the latter will grow stronger, eventually will start giving rise to impressive solar events anew, and “cycle 25” will begin for good. (Personally I have a special interest in this one since a model I’ve developed predicts serious flares to most likely start in early April. If you are curious you can read about it here.)

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