Tag Archives: new discovery

Astronomers detect hot gas bubble swirling around the Milky Way’s black hole

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Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have spotted signs of a ‘hot spot’ orbiting Sagittarius A*, the black hole at the centre of our galaxy. The finding helps us better understand the enigmatic and dynamic environment of our supermassive black hole.

“We think we’re looking at a hot bubble of gas zipping around Sagittarius A* on an orbit similar in size to that of the planet Mercury, but making a full loop in just around 70 minutes. This requires a mind blowing velocity of about 30% of the speed of light!” says Maciek Wielgus of the Max Planck Institute for Radio Astronomy in Bonn, Germany, who led the study published today, Sept 22, 2022 in Astronomy & Astrophysics.

The orbit of the hot spot around Sagittarius A*

The observations were made with ALMA in the Chilean Andes — a radio telescope co-owned by the European Southern Observatory (ESO) — during a campaign by the Event Horizon Telescope (EHT) Collaboration to image black holes. In April 2017 the EHT linked together eight existing radio telescopes worldwide, including ALMA, resulting in the recently released first ever image of Sagittarius A.

To calibrate the EHT data, Wielgus and his colleagues, who are members of the EHT Collaboration, used ALMA data recorded simultaneously with the EHT observations of Sagittarius A. To the team’s surprise, there were more clues to the nature of the black hole hidden in the ALMA-only measurements.

By chance, some of the observations were done shortly after a burst or flare of X-ray energy was emitted from the centre of our galaxy, which was spotted by NASA’s Chandra Space Telescope. These kinds of flares, previously observed with X-ray and infrared telescopes, are thought to be associated with so-called ‘hot spots’, hot gas bubbles that orbit very fast and close to the black hole.

The flares were long thought to originate from magnetic interactions in the very hot gas orbiting very close to Sagittarius A*, and the new findings support this idea. “Now we find strong evidence for a magnetic origin of these flares and our observations give us a clue about the geometry of the proces,” says co-author Monika Mościbrodzka from Radboud University.

The observations confirm some of the previous discoveries made by the GRAVITY instrument at ESO’s Very Large Telescope (VLT), which observes in the infrared. The data from GRAVITY and ALMA both suggest the flare originates in a clump of gas swirling around the black hole at about 30% of the speed of light in a clockwise direction in the sky, with the orbit of the hot spot being nearly face-on.

Move over plain helium, Pionic helium is here

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A helium atom in which one of the two electrons has been replaced by a negative pion gives out a composite particle made of one quark and one antiquark. Exotic atoms can help physicists to make exquisitely precise measurements of the fundamental constants of nature, such as the size of the proton.

Pionic helium is the latest addition to a zoo of exotic atoms, including positronium, muonium, muonic hydrogen, muonic deuterium and antihydrogen. No dilithium crystals yet, though. Pionic helium could provide a direct measurement of the mass of a related fundamental particle, the neutrino. That has been estimated indirectly, says physicist Masaki Hori, but “it is always nice to have a direct laboratory determination”.

Exotic atoms are those in which one or more of the constituents of normal atoms have been replaced by an exotic particle, such as an antimatter particle. These atoms can then be probed to search for any tiny discrepancies in their properties from those predicted by models using techniques that underpin the world’s most accurate timekeepers, atomic clocks — and thereby opening a window on the foundations of physics.

Transition in ‘pionic’ helium atom

Reporting for the the first time about laser excitation of helium atoms in which one electron has been replaced by a subatomic particle called a pion, the scientists said they recorded a transition in a ‘pionic’ helium atom, in which one of the two electrons of a helium atom has been replaced by a subatomic particle called a pion.

Pions were discovered7 by Cecil Powell and co-workers in 1947, but their existence was first predicted in 1935 by Hideki Yukawa. They belong to the family of subatomic particles known as mesons, which are made up of a quark and an antiquark. Quarks are the particles that make up protons and neutrons.

Pions are short-lived particles that come in positively charged, negatively charged and neutral varieties and the team amanged to produce negatively charged pions with a lifetime of only 26 nanoseconds when isolated. It is thus no small feat that the experiment not only succeeded in replacing an electron in helium atoms with a pion, but also observed the resulting exotic atom undergo a quantum transition.

Hori and colleagues’ work now opens up a whole new experimental system for further exploration. If some challenges can be overcome, such exploration might enable the accuracy of the mass of the negative pion to be improved by a factor of 10–100, for instance; currently, this mass is known to only six decimal places.