Enlarge / A new image from the Event Horizon Telescope has revealed powerful magnetic fields spiraling from the edge of a supermassive black hole at the center of the Milky Way, Sagittarius A*. (credit: EHT Collaboration)

Physicists have been confident since the1980s that there is a supermassive black hole at the center of the Milky Way galaxy, similar to those thought to be at the center of most spiral and elliptical galaxies. It's since been dubbed Sagittarius A* (pronounced A-star), or SgrA* for short. The Event Horizon Telescope (EHT) captured the first image of SgrA* two years ago. Now the collaboration has revealed a new polarized image (above) showcasing the black hole's swirling magnetic fields. The technical details appear in two new papers published in The Astrophysical Journal Letters. The new image is strikingly similar to another EHT image of a larger supermassive black hole, M87*, so this might be something that all such black holes share.

The only way to "see" a black hole is to image the shadow created by light as it bends in response to the object's powerful gravitational field. As Ars Science Editor John Timmer reported in 2019, the EHT isn't a telescope in the traditional sense. Instead, it's a collection of telescopes scattered around the globe. The EHT is created by interferometry, which uses light in the microwave regime of the electromagnetic spectrum captured at different locations. These recorded images are combined and processed to build an image with a resolution similar to that of a telescope the size of the most distant locations. Interferometry has been used at facilities like ALMA (the Atacama Large Millimeter/submillimeter Array) in northern Chile, where telescopes can be spread across 16 km of desert.

In theory, there's no upper limit on the size of the array, but to determine which photons originated simultaneously at the source, you need very precise location and timing information on each of the sites. And you still have to gather sufficient photons to see anything at all. So atomic clocks were installed at many of the locations, and exact GPS measurements were built up over time. For the EHT, the large collecting area of ALMA—combined with choosing a wavelength in which supermassive black holes are very bright—ensured sufficient photons.

Enlarge / Close up of the 11th century Verona astrolabe showing Hebrew (top left) and Arabic inscriptions. (credit: Federica Gigante)

Cambridge University historian Federica Gigante is an expert on Islamic astrolabes. So naturally she was intrigued when the Fondazione Museo Miniscalchi-Erizzo in Verona, Italy, uploaded an image of just such an astrolabe to its website. The museum thought it might be a fake, but when Gigante visited to see the astrolabe firsthand, she realized it was not only an authentic 11th century instrument—one of the oldest yet discovered—it had engravings in both Arabic and Hebrew.

“This isn’t just an incredibly rare object. It’s a powerful record of scientific exchange between Arabs, Jews, and Christians over hundreds of years,” Gigante said . “The Verona astrolabe underwent many modifications, additions, and adaptations as it changed hands. At least three separate users felt the need to add translations and corrections to this object, two using Hebrew and one using a Western language.” She described her findings in a new paper published in the journal Nuncius.

As previously reported, astrolabes are actually very ancient instruments—possibly dating as far back as the second century BCE—for determining the time and position of the stars in the sky by measuring a celestial body's altitude above the horizon. Before the emergence of the sextant, astrolabes were mostly used for astronomical and astrological studies, although they also proved useful for navigation on land, as well as for tracking the seasons, tide tables, and time of day. The latter was especially useful for religious functions, such as tracking daily Islamic prayer times, the direction of Mecca, or the feast of Ramadan, among others.

Enlarge (credit: ASI/NASA )

In 2022, NASA's Double Asteroid Redirect Test (DART) smashed into the asteroid Dimorphos in a successful test of planetary defense technology. That success was measured by a significant shift in Dimorphos' orbit around the larger asteroid Didymos. Since then, a variety of observatories have been analyzing the data to try to piece together what the debris from the impact tells us about the structure of the asteroid.

All of those observations have taken place at great distances from the impact. But DART carried a small cubesat called LICIACube along for the ride and dropped it onto a trailing trajectory a few weeks before impact. It took a while to get all of LICIACube's images back to Earth and analyzed, but the results are now coming in, and they provide hints about Dimorphos' composition and history, along with why the impact had such a large effect on its orbit.

Tracing debris

LICIACube had both narrow and widefield imagers on board (named LEIA and LUKE via some carefully chosen backronyms). It trailed DART through the impact area by about three minutes and captured images starting about a minute before the impact and continuing for over five minutes afterward.

Enlarge (credit: ESO/M. Kornmesser )

Quasars initially confused astronomers when they were discovered. First identified as sources of radio-frequency radiation, later observations showed that the objects had optical counterparts that looked like stars. But the spectrum of these ostensible stars showed lots of emissions at wavelengths that didn't seem to correspond to any atoms we knew about.

Eventually, we figured out these were spectral lines of normal atoms but heavily redshifted by immense distances. This means that to appear like stars at these distances, these objects had to be brighter than an entire galaxy. Eventually, we discovered that quasars are the light produced by an actively feeding supermassive black hole at the center of a galaxy.

But finding new examples has remained difficult because, in most images, they continue to look just like stars—you still need to obtain a spectrum and figure out their distance to know you're looking at a quasar. Because of that, there might be some unusual quasars we've ignored because we didn't realize they were quasars. That's the case with an object named J0529−4351, which turned out to be the brightest quasar we've ever observed.