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Category: cosmology – Page 2

Could we send a spacecraft to a black hole?

Black holes represent some of the most extreme environments in the universe. They are the sources of the strongest gravitational fields, allowing us to test Einstein’s theory of general relativity to an extent impossible with small objects. But we are also reaching the limit of what we can learn about one remotely. So, various authors have put forward ideas for how we might eventually send a probe directly to a black hole to observe it up close. One of the most vocal of those authors is Cosimo Bambi of Fudan University in Shanghai—and he recently released a paper, available as a preprint on arXiv, about what it would take to send a gram-sized probe to a nearby black hole.

Unfortunately, we do not know of any “nearby” ones—at least not yet. The closest known black hole is Gaia BH1, which is roughly 1,560 light-years away in the constellation Ophiuchus. However, we only know Gaia BH1’s position because it has a slight gravitational pull on a nearby companion star. There are likely many more invisible black holes in our galactic neighborhood that do not have such telltale signs.

According to the paper, the Milky Way likely contains about 100 million stellar-mass black holes. That is not a typo—there are most likely hundreds of millions of black holes the size of a star floating around our galaxy. Crucially, 92% of them are isolated, without a companion star to illuminate them—meaning they would be essentially invisible because they suck up all the light directed their way. But, according to Bambi’s paper, there should be one stellar-mass black hole for roughly every 1,500 cubic parsecs (about 52,000 cubic light-years)—keep in mind that the Milky Way has an estimated volume of 150 cubic kiloparsecs.

DESI releases biggest 2D map of the universe

Hold on to your telescopes: The DESI Legacy Imaging Surveys team has released the largest-ever 2D color map of the universe. The 5.6-trillion-pixel map contains nearly 4 billion celestial objects, primarily stars and galaxies. The data is available for all to use and publicly view through the Legacy Survey Sky Viewer.

Astronomers and citizen scientists can explore the map or combine it with their own observations to better understand our universe. Researchers can search for rare phenomena like gravitational lenses, observe fleeting events like supernovae, and investigate two of physics’ biggest mysteries: dark matter, the invisible substance that accounts for most of the mass in our universe, and dark energy, the force driving our universe’s accelerating expansion.

The new map builds on earlier versions from the DESI Legacy Imaging Surveys that have already proved invaluable. To date, more than 1,800 science papers that reference the Legacy Surveys data have been published.

An ultramassive white dwarf half Earth’s size may hold a rare oxygen-neon core

Astronomers have found evidence that one of the most massive white dwarfs known has an oxygen-neon core instead of the more common carbon-oxygen core. The finding is important because the composition of a white dwarf’s core determines how it will evolve. A paper outlining this discovery was published in The Astrophysical Journal.

Typically, white dwarfs have a mass of 0.5–0.7 times the sun’s mass. Such objects have a core made up mainly of carbon and oxygen (C/O core). When they have stellar companions, these dense objects can accumulate matter from them and eventually produce a Type Ia supernova. Ultramassive white dwarfs, with masses above roughly 1.05–1.1 times the sun’s mass, tell a different story that is not yet fully understood.

These more massive white dwarfs are thought to form from “ancestor” or progenitor stars in the range of about 8–10 times the sun’s mass. In these heavier progenitors, the core reaches higher temperatures and densities, allowing carbon to ignite and fuse further into oxygen and neon (O/Ne core). This does not happen in the cores of lower-mass stars, which stop fusing once they have built up carbon and oxygen, lacking the required core temperatures.

Astronomers catch massive galaxy assembling piece by piece 1.2 billion years after Big Bang

Astronomers have discovered a remarkably tiny group of six young galaxies just 1.2 billion years after the Big Bang. This may be a rare glimpse of how some of the universe’s largest galaxies formed. The paper outlining the findings was submitted to the arXiv preprint server on July 13.

Chaotic patches The widely accepted cosmological model of the universe known as the Lambda Cold Dark Matter Model suggests that galaxies primarily form hierarchically through mergers. That means they grow piece by piece, as smaller galaxies merge over billions of years. In this context, dense regions in the early universe serve as natural laboratories to test this idea.

These dense patches, known as protoclusters and proto-groups, are young clusters of galaxies packed into a region just tens of thousands of light-years across and represent an especially brief and extreme stage in galaxy evolution. Spotting them requires telescopes sensitive enough to detect faint, low-mass galaxies at extreme distances, and precise enough to confirm that the galaxies are truly bound together.

XENONnT detector narrows the hunt for dark matter

Using a detector filled with nearly 9 metric tons of liquid xenon, researchers have delivered some of the most sensitive dark matter results ever recorded. In the latest analysis from the XENON collaboration, working at the Gran Sasso National Laboratory in Italy, researchers carried out a “blind” test to avoid bias in measurements of the XENONnT detector, pushing the experiment’s sensitivity to unprecedented levels.

Their results have been published in Physical Review Letters and could now tighten the net around several of the leading candidates for the true nature of dark matter.

Galactic spins carry fingerprints of the primordial universe

The origin of spin in spiral and elliptical galaxies has posed a long-standing puzzle for astronomers. One idea, known as tidal torque theory, proposes that galaxies’ spins are an imprinted record of the early universe, imparted by gravity long before galaxies first formed and still detectable in galaxies today.

Through new research published in Nature Astronomy, a team led by Ming-Jie Sheng at Xiamen University has put that idea to its toughest test yet.

JWST study suggests a handful of ‘leaky’ galaxies reionized the early universe

A new study analyzing the James Webb Space Telescope (JWST) spectra of more than 1,400 galaxies suggests a surprisingly small group of “leaky” galaxies was responsible for cosmic reionization. The paper outlining this work was posted to the arXiv preprint server on July 24.

Cosmic reionization happened when ionizing ultraviolet radiation from early stars and galaxies heated the universe’s neutral hydrogen gas and converted it into the ionized state seen today. Based on cosmic microwave background and quasar data, this epoch is estimated to have occurred around redshift 6–8, roughly 600 million to 1 billion years after the Big Bang. The main driver is thought to be star-forming galaxies. Therefore, the epoch of reionization is considered the last major phase transition of the universe.

The ultraviolet radiation responsible for cosmic reionization is mainly composed of Lyman continuum (LyC) photons with wavelengths less than 912 Å. Their escape fraction from galaxies, along with the rate of their production, determines whether they reach and ionize the intergalactic medium because most LyC photons are absorbed internally by gas and dust.

Using the Earth’s magnetic field to hunt for axions and dark photons

Dark matter’s existence is all but certain—astronomers believe it makes up about a quarter of the universe’s total energy content—yet its true identity has eluded us for decades. Two of the leading candidates for dark matter are the hypothetical particles ultralight axions and dark photons, which in the range studied here would be some 19 to 21 orders of magnitude lighter than the electron.

Conventional axion searches tend to involve converting them into photons with the help of strong laboratory magnets. However, research in a laboratory inherently limits the space over which such a field can be applied.

A collaborative team of researchers from Kyoto University, Hiroshima University and Nihon University realized that, by contrast, Earth’s own magnetic field spans a scale no laboratory could match. Their paper is published in the journal Progress of Theoretical and Experimental Physics.

Chinese observatory identifies most powerful cosmic particle accelerator ever detected

Researchers working at the Large High Altitude Air Shower Observatory (LHAASO) in China’s Sichuan Province have discovered that the unique binary system Cygnus X-3, located in the constellation Cygnus, is the most powerful particle accelerator known to date. The findings were reported by Xinhua News Agency, a TV BRICS partner, citing the Institute of High Energy Physics of the Chinese Academy of Sciences.

Cygnus X-3 is a binary system consisting of either a black hole or a neutron star and a massive companion star. The compact object actively accretes material from the powerful stellar wind of its companion, accelerating particles to extremely high energies.

Scientists had previously believed that charged particles within the Milky Way could reach energies of around one petaelectronvolt (PeV). However, a detailed analysis of ultra-high-energy gamma-ray emissions enabled LHAASO researchers to determine that Cygnus X-3 is capable of accelerating cosmic rays to energies of at least 30 petaelectronvolts. The team also detected a periodic ultra-high-energy gamma-ray signal with a cycle of 4.8 hours and established that the particle acceleration region is located approximately three solar radii from the source of the radiation.

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