The universe that you see when you look out the night sky isn’t the complete picture. All the cosmic objects in the universe—stars, black holes, galaxies, what have you—shine with many forms of light, only some of which you can see. This is because “visible” light only exists as a small sliver in the vast catalog known as the electromagnetic spectrum.
Most of the stuff in the sky shines in wavelengths either below or above what we can see. This applies to nearly all cosmic bodies. In fact, it’s this fact that scientists in radio telescopes, like the one in the South Africa Radio Astronomy Observatory (SARAO), constantly take advantage of when viewing the sky. Oftentimes, astronomers actually manage to find the light that these bodies emit before they find the bodies themselves.
This appears to be the case with a recent find by scientists from SARAO; together with the Commonwealth Scientific and Industrial Research Organization (CSIRO)’s Australian Square Kilometer Array Pathfinder (ASKAP) and SARAO’s MeerKAT radio telescope, scientists found a peculiar source of radio waves emanating from near the center of the Milky Way Galaxy, called the easy-to-remember ASKAP J173608.2-321635. The study is currently available in preprint at arXiv.
ASKAP’s Variables and Slow Transients (VAST) survey actually found the odd radio source and detected it six (6) times, hence the name of the cosmic mystery. (The numbers trailing its name are its coordinates in the sky.) Astronomers then aimed SARAO’s MeerKAT telescope at it for three months starting from November of 2020, at a 2-4-week interval.
Ziteng Wang, Ph.D. student from the Sydney Institute for Astronomy (SIA) at the University of Sydney, CSIRO, and the ARC Center of Excellence for Gravitational Wave Discovery (OzGrav)—together with a team of scientists—screened the results obtained from aiming their radio telescopes at the peculiar ASKAP radio source, and couldn’t find any matches with what the team expected from certain celestial bodies, like pulsars and supernovae. The team also tried identifying the source with visible light, yet still found nothing.
Said Wang: “The strangest property of the signal […] is that it has a very high polarization […] [meaning] its light oscillates in only one direction, but that direction rotates with time.” Wang added: “The brightness of the object also varies dramatically, by a factor of 100, and the signal switches on and off apparently at random. We’ve never seen anything like it.”
“This object was unique in that it started out invisible, became bright, faded away and then reappeared. This behavior was extraordinary,” said SIA astronomer Prof. Tara Murphy, who’s also from OzGrav.
Prof. David Kaplan, from the University of Wisconsin-Milwaukee, noted that the find seems more aligned towards mysterious radio sources known as Galactic Center Radio Transients (GCRTs).
“While […] ASKAP J173608.2-321635 does share some properties with GCRTs, there are also differences. And we don’t really understand those sources, anyway, so this adds to the mystery.”
(For more mysterious space finds, some unexplained data from the XENON1T dark-matter detector might just be the evidence we’re looking for in the search for dark energy. For another, here’s our piece on the “accidental” brown dwarf find that’s zooming through the galaxy.)
References
- Sci-News. (2021, October 12). Astronomers Find Strange Source of Radio Waves near Milky Way’s Center. Sci-News. http://www.sci-news.com/astronomy/radio-source-milky-ways-center-10157.html
- Wang, Z., Kaplan, D. L., Murphy, T., Lenc, E., Dai, S., Barr, E., Dobie, D., Gaensler, B. M., Heald, G., Leung, J. K., O’Brien, A., Pintaldi, S., Pritchard, J., Rea, N., Sivakoff, G. R., Stappers, B. W., Stewart, A., Tremou, E., Wang, Y., … Zic, A. (2021). Discovery of askap j173608. 2-321635 as a highly-polarized transient point source with the australian ska pathfinder. ArXiv:2109.00652 [Astro-Ph]. http://arxiv.org/abs/2109.00652
