Totality darkens the sky; Hubble finds a stellar stream tracing dark matter
A total eclipse darkened northern skies as Hubble found a dark-matter-tracing stellar stream; James Webb revealed gas-wrapped black-hole candidates, while simulations suggested that planetary building blocks could form early.
Science··Midday
The moon's shadow ran south to the Mediterranean
The moon's shadow drew a 293 kilometre wide band from the Arctic Ocean to the Mediterranean on 12 August. Totality began near Siberia, crossed eastern Greenland, western Iceland and northern Spain, passed the Balearic Islands and ended over the Mediterranean at sunset. People inside the track could see the corona, the sun's outer atmosphere, with the naked eye. Space.com skywatching editor Daisy Dobrijevic watched from a ship in Scoresby Sund, Greenland, and reported Jupiter, Mercury and Venus appearing in the darkened sky beside a large solar prominence. A much wider region outside totality saw the same event in partial form. The moon covered part of the solar disk across Europe and Scandinavia, the northeastern United States, much of Canada and Alaska. The day's most immediate event in the sky was a few minutes of darkness that drew millions of faces upward. Elsewhere in the science news, more distant light offered a different kind of view: traces that let researchers reconstruct the histories of stars and galaxies rather than watch one celestial alignment unfold in real time.[1]
A faint stellar trail makes dark matter measurable
A faint trail around the ultra-diffuse galaxy UGC9050-Dw1 in Hubble Space Telescope images has become the first globular-cluster stellar stream identified outside the Milky Way. Such streams are long, thin traces left as gravity pulls stars away from a cluster during its journey through a galaxy. A University of Copenhagen team modelled the stream's motion to measure the mass distribution of UGC9050-Dw1 and concluded that the galaxy contains substantial dark matter, in line with earlier work. The method does not photograph dark matter directly. It reads the gravitational effect of invisible mass in the shape and movement of the stellar trail. Applying an approach used in the Milky Way to a globular-cluster stream in another galaxy suggests that similar traces could become mass gauges across different galaxy types. The result currently rests on one galaxy. The researchers expect the Euclid and Nancy Grace Roman space telescopes to find more streams and move the method from a single example to a broader galactic population.[2]
Two surprising beginnings at cosmic dawn
Objects known as little red dots in James Webb Space Telescope images may point to an unusual structure between a star and a black hole in the early universe. A Nature study examines MoM-BH*-1 as it appeared 660 million years after the Big Bang and argues that the dots could be black holes wrapped in dense gas. According to the work led by Rohan Naidu, each object is at least 100,000 times larger than our sun, and the dots appear in nearly every surveyed region covering the universe's first 1.5 billion years. A Nature commentary treats the result as an important clue while the formation of these black hole stars remains under theoretical debate. Another study uses simulations to propose that rocky planetary building blocks could form around low-mass, long-lived stars in gas clouds enriched by the first supernovae only 100 million years after the Big Bang. The modelled disk contains several Earth masses of solid material and a notable amount of water for such an early setting. This second result is not an observation; it comes from a computer-simulation preprint on arXiv that has been accepted by The Astrophysical Journal Letters. Together, the developments make the young universe look busier: enormous candidate black holes inside gas cocoons on one scale, and the first small building blocks capable of becoming rocky worlds on another.[3], [4]
