Probe this invisible cosmic enigma with a DIY radio telescope
Category: cosmology – Page 6
Mysterious Cygnus Bubble may trace back to microquasar, astronomers suggest
Astronomers have proposed a new explanation for the mysterious Cygnus Bubble, a vast cloud of ultra-high-energy gamma rays stretching thousands of light-years across the sky. While the bubble has generally been linked to the Cygnus X star-forming region, the new study argues that a microquasar more naturally explains its highest-energy emission. The results were published in a paper in The Astrophysical Journal Letters on July 21.
For years, astronomers have puzzled over the sources of the highest-energy cosmic rays in our galaxy—particles accelerated to a quadrillion electron volts, or a petaelectronvolt (PeV; that’s 15 zeros after 1). These sources are called Galactic PeVatrons, and they are notoriously hard to pin down. In principle, all kinds of astrophysical objects violent enough to accelerate particles to extreme energies could be PeVatrons: supernova remnants, pulsar wind nebulae, star clusters or binary star systems.
The accelerated particles travel outward and light up with ultra-high-energy gamma rays wherever they eventually slam into ambient gas, sometimes hundreds to thousands of light-years from their true source. One of the most striking gamma-ray structures in the sky, the “Cygnus Bubble,” has long been attributed to a nearby cluster of massive, young stars in the Cygnus X star-forming region, some 4,600 light-years away.
Astronomers Caught a Star Exploding Almost the Instant It Began
Astronomers witnessed a star’s death almost from the instant it began, catching an extraordinarily rare X-ray flash as a supernova erupted 500 million light-years away.
Astronomers rarely get to watch a star die from the beginning. Usually, a supernova is discovered only after the explosion is already well underway.
SN 2026gzf was different.
Stellar stream beyond Milky Way offers new tool to map dark matter
In the image above, a faint trail of stars can be seen stretching across the galaxy. These structures, known as globular cluster stellar streams, are coherent stellar structures that retain a record of their dynamical history and can provide unique insights into the evolution of galaxies and the nature of dark matter.
Globular cluster stellar streams offer astronomers a unique opportunity to map otherwise invisible dark matter and study how it behaves. For many years, they have been difficult to observe because they are extremely faint. However, advances in large astronomical data sets and sophisticated analysis techniques have recently made stellar streams one of the most promising tools in galactic astronomy.
Now, Ph.D. student Julie Kiel Holm from the Niels Bohr Institute and associate professor Sarah Pearson from DTU Space, together with an international team of researchers, have made a discovery that has never been seen before. Their findings have just been published in Nature.
Famous oddball quasar isn’t X-ray weak after all, astronomers say
For more than two decades, the quasar PHL 1811 has been considered the prototype of a rare class of “intrinsically X-ray weak” quasars, thought to produce unusually little X-ray radiation. But in 2024, the Einstein Probe spacecraft caught the object in a bright X-ray flare. In a new study, astronomers combined that observation with more than 20 years of archival data to revisit the mystery. The findings were published in The Astrophysical Journal on July 28.
In active galactic nuclei (AGN), material spiraling into the central black hole releases enormous amounts of energy. The accretion disk—the swirling ring of hot gas around the black hole—releases this energy primarily in optical and ultraviolet (UV) light. Additionally, a separate region of extremely hot plasma, called the corona, sits above the disk and is responsible for the X-ray emission. The link between these two emissions is well established.
A rare subset of AGNs breaks this pattern, appearing far dimmer in X-rays than expected, often linked to black holes feeding faster than the theoretical limit. This could mean either that gas is blocking the X-rays without dimming the optical/UV, or that it is “intrinsically weak” as the X-ray-emitting corona itself is genuinely suppressed.
Astronomers discover a new kind of cosmic object — a black hole ‘star’
Have you heard of the inexplicable little red dots which were found in images from the early universe?
This article may explain them — _____________
The object was lurking in the constellation of Cetus, the Whale, billions of light years from Earth. It is thought to have formed 660m years after the big bang, astronomers’ leading theory as to how the universe began.
Measurements of the exotic body found that while it resembles an immense star, it releases 100bn times more energy than any known star can produce. The energy output is far closer to that observed from black holes than stars.
“We have found a new type of astrophysical object, a black hole star,” said Dr Rohan Naidu at the Kavli Institute for Astrophysics and Space Research, part of the Massachusetts Institute of Technology.
It “shines with the energy typically associated with black holes, but at the same time bears signatures classically associated with stars”, he added.”
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.