Astronomers have discovered an extraordinary celestial object in the galaxy NGC 4945, located about 12 million light-years from Earth. This object, dubbed “Punctum” (Latin for “point”), is a highly compact radio beacon emitting a uniquely clean and stable signal, distinguished by an almost unprecedented degree of linear polarization—about 50% at millimeter wavelengths near 100 GHz. This is a significant scientific anomaly because such high polarization implies a strikingly uniform magnetic field in the region from which it originates, a condition rarely observed in cosmic sources where mixed magnetic fields typically scramble and average out polarization signals. Researchers first detected Punctum using Chile’s Atacama Large Millimeter/submillimeter Array (ALMA) during an observation campaign of NGC 4945’s active starburst core.
Unlike a typical pulsar, which emits periodic, pulselike signals, Punctum is steady, making it unique among known types of neutron stars and radio sources. It is also uncharacteristically invisible at other wavelengths, with no equivalent emission detected by Chandra X-ray Observatory or the Australia Telescope Compact Array at radio frequencies, rendering it a true outlier in available cosmic catalogs.
The discovery team, led by Dr. Elena Shablovinskaia of the Instituto de Estudios Astrofísicos at Universidad Diego Portales, notes that current hypotheses for Punctum’s identity include a young, highly magnetized neutron star (like a magnetar), a newborn supernova remnant with extreme field alignment, or perhaps an unusually magnetized massive star. However, Punctum’s persistent signal and lack of pulsation challenge direct classification. Its polarization approaches the theoretical maximum for synchrotron emission in a perfectly ordered magnetic field, indicating an environment of remarkable structural stability and posing an intriguing theoretical challenge.
The significance of this discovery extends beyond classifying a new source. The highly polarized signal acts as a probe of the galaxy’s magnetic fields, enabling astronomers to map invisible magnetism that influences star formation, gas dynamics, and energy flow within galaxies. The object’s discovery hints that other such highly polarized but otherwise hidden radio beacons could exist, especially within the dust-shrouded centers of star-forming galaxies, and might represent an overlooked population of energetic objects immensely important to galactic evolution and magnetic dynamics.
Punctum’s detection opens the door to a new kind of galactic mapping, using millimeter-wave polarimetry to chart the magnetic “skeleton” that shapes galaxies from within. Its existence suggests that standard surveys may be missing key actors in the universe’s energetic theater, especially in environments opaque to optical, X-ray, or conventional radio telescopes.
Future research plans include coordinated, multiwavelength observational campaigns with ALMA, high-resolution radio interferometry, sensitive radio imaging, and possible infrared studies with the James Webb Space Telescope. These efforts aim to reveal Punctum’s full nature by monitoring for variability (which could confirm a pulsar or spinning neutron star), exploring its spectrum, and searching for potential infrared or lower-frequency counterparts.
For now, Punctum remains an enigmatic beacon, challenging existing astrophysical models and offering new ways to explore the fundamental role of magnetic fields in shaping galaxies. Its discovery invites astronomers to look for more such celestial signposts, potentially transforming the understanding of hidden processes in galactic centers.
More information is available here.
Image above: Galaxy named NGC 4945. X-ray: NASA/CXC/Univ degli Studi Roma Tre/A.Marinucci et al. Optical: ESO/VLT & NASA/STScI
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