Silent Explosion: The Faintest Supernova in the Galaxy ⚡ экспресс
First deep radio observations of the Pa 30 nebula—a candidate supernova remnant from a white dwarf merger in 1181—were performed at 1.5 and 6 GHz. No diffuse radio emission or emission from a central source was detected; 3σ upper limits on the flux density were set at 0.84 mJy (1.5 GHz) and 0.29 mJy (6 GHz). The surface radio brightness of Pa 30 is roughly 3 orders of magnitude lower than that of typical supernova remnants with comparable angular sizes. Assuming 10% of the supernova kinetic energy goes into cosmic rays, the lack of synchrotron emission implies a kinetic energy of ≲3×10⁴⁷ (B/10 μG)^-1.65 erg—3–4 orders of magnitude below typical values and a record low among Galactic remnants. This points to inefficient particle acceleration. Such a low energy either suggests a population of radio-faint, sub-energetic remnants in the Galaxy, or challenges the interpretation of Pa 30 as a supernova remnant.
In 1181, in the constellation Cassiopeia, a "guest star" blazed into view — a bright spot that rivaled other luminaries for half a year. Most likely, it was the merger of two white dwarfs, the burned-out remnants of stars like our Sun. What remains is nebula Pa 30: a cloud of tenuous gas and cosmic dust, expanding at a breakneck pace — nearly 5% the speed of light. Yet modern radio telescopes pick up only a faint whisper instead of the expected roar.
Typically, a supernova's shockwave accelerates charged particles to near-light speeds, making them "scream" in radio waves. Pa 30 is silent — its radio emission is a thousand times weaker than that of the Crab Nebula with a neutron star inside. This means either the explosion was surprisingly sluggish, or particle acceleration works differently. It’s precisely this scenario — a white dwarf merger without a powerful radio echo — that Subrahmanyan Chandrasekhar predicted back in the 1930s while studying the mass limit of these objects.
The most unexpected conclusion: our Galaxy may be littered with dozens of such invisible ghosts. We simply hadn't noticed them, and now we’ll have to rewrite the history of stellar explosions in the Milky Way.
🎯 Pa 30 is one of the few nebulae that can be linked to historical records: its outburst was observed in 1181 in the constellation Cassiopeia, and it hung in the sky for nearly half a year.