No massive black holes in the Milky Way halo.

The gravitational wave detectors have shown a population of massive black holes that do not resemble those observed in the Milky Way and whose origin is debated. According to a possible explanation, these black holes may have formed from density fluctuations in the early Universe (primordial black holes), and they should comprise several to 100% of dark matter to explain the observed black hole merger rates. If these black holes existed in the Milky Way dark matter halo, they would cause long-timescale gravitational microlensing events lasting years.

Newly formed dust within the circumstellar environment of SN Ia-CSM 2018evt.

Dust associated with various stellar sources in galaxies at all cosmic epochs remains a controversial topic, particularly whether supernovae play an important role in dust production. We report evidence of dust formation in the cold, dense shell behind the ejecta-circumstellar medium (CSM) interaction in the Type Ia-CSM supernova (SN) 2018evt three years after the explosion, characterized by a rise in mid-infrared emission accompanied by an accelerated decline in the optical radiation of the SN. Such a dust-formation picture is also corroborated by the concurrent evolution of the profiles of the Hα emission line.

Minutes-duration optical flares with supernova luminosities.

In recent years, certain luminous extragalactic optical transients have been observed to last only a few days. Their short observed duration implies a different powering mechanism from the most common luminous extragalactic transients (supernovae), whose timescale is weeks. Some short-duration transients, most notably AT2018cow (ref.