The latest in Ph-word: June 2020

Last month our usual suspects were all here: dark matter, black holes, distant stars, cheap energy. (Wait, what?)

The potentially big news of the month was a handful of excess events in XENON1T. And I explain.

XENON1T is one of the experiments hoping to find dark matter directly. That is, some of the particles making up dark matter will grace the detector by colliding with it. In the previous years this meant that dark matter should kick atomic nuclei out of their positions, but this research didn’t turn up anything; so the experiment started looking for lighter dark matter, which would kick electrons out of their orbits in atoms.

XENON1T ran with this goal for one year, and finally came up with a promising signal for the first time. It saw exactly what it would if electrons were kicked out by axions coming from the sun’s core. (Axions are the hypothesized particles that you’ll hear more and more of in the next few years, as they are almost the only proposed candidate for dark matter that hasn’t been mostly wiped out by experiments by now.)

Of course this signal sounds too good and too feeble to be true and nobody is partying yet. There is always the possibility that it came from a mundane source, such as tiny amounts of natural radioactivity. The way to go is to wait for a few years more and let XENON1T and a couple of similar experiments repeat the measurement, and see if the signal keeps appearing or if it was due to some boring incident.


In other news, we have the first two photos ever of a starscape looking different than from earth.

NASA’s New Horizons, best known for exploring Pluto a few years ago, left earth in 2006 and is now found in the Kuiper Belt, the huge asteroid zone beyond Neptune’s orbit.

That means that New Horizons is currently seven billion kilometers away from us. This is far away, so far actually that the positions of stars begin looking shaken.

Specifically, the spacecraft’s photos of Proxima Centauri -the nearest star just four light years away- and Wolf 359 -a star in the constellation of Leo at eight light years- are very visibly different than terrestrial ones. (You can even put on your red-and-blue glasses and see the two stars in stereo, in photos created from New Horizons data by famous astronomer Brian May.)


After everything that the LIGO and Virgo detectors of gravitational waves have accomplished, one thing eventually managed to surprise them.

That thing was supposed to be one of their bread-and-butter “mergers”, where two black holes, or two neutron stars, or one hole and one neutron star, become one and send tremendous gravitational waves across space. But this time was different.

This time one of the two partners that were caught merging, 800 million light years away, looked indeed like a black hole weighing 23 times the sun. The second partner though looked as having 2.6 times the mass of the sun.

This can be a problem, because neutron stars are known to have less than twice the solar mass; and black holes in such binary systems have at least five times said mass.

That’s a new small mystery for astrophysics, which in the simplest case might result in changing what we know for one of these kinds of objects and in the most complicated case might bring about the next cool thing.


And now for something different: a generator using a new way of producing energy was just developed.

Researchers in the National University of Singapore found how to pump a little energy out of shadow. More specifically, they made a silicon wafer with gold strips on top and put it half in the sun and half under shade. The contrast in illumination caused a difference in voltage between the two areas, resulting in the flow of electric current.

So far the device can only power something as small as a digital watch but it’s still a good start. If its efficiency and price get improved, the motion of tree branches and of the sun in the sky could one day send us an energy boost.

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