Tag: space exploration

There are currently hundreds of fast radio bursts, and scientists have assembled mounting evidence to explain what triggers them: highly magnetised neutron stars known as magnetars (neutron stars are a type of dead star).

Now, Caltech-led researchers have uncovered where fast radio bursts (FRBs) are more likely to occur in the Universe – in massive star-forming galaxies rather than low-mass ones.

This finding has led to new ideas about how magnetars themselves form. Specifically, the work suggests that these exotic dead stars, whose magnetic fields are 100 trillion times stronger than Earth’s, often form when two stars merge and later blow up in a supernova.

Previously, it was unclear whether magnetars formed in this way from the explosion of two merged stars or whether they might form when a single star explodes.

The hidden secrets of magnetars

“The immense power output of magnetars makes them some of the most fascinating and extreme objects in the universe,” said Kritti Sharma, lead author of the new study.

“Very little is known about what causes the formation of magnetars upon the death of massive stars, but our work helps to answer this question.”

The project began by searching for fast radio bursts using the Deep Synoptic Array-110 (DSA-110), a Caltech project funded by the National Science Foundation and based at the Owens Valley Radio Observatory near Bishop, California.

The sprawling radio array has detected and localised 70 FRBs to their specific galaxy of origin (only 23 other FRBs have been localised by other telescopes). In the current study, the researchers analysed 30 of these localised FRBs.

How fast radio bursts occur in galaxies

Although fast radio bursts are known to occur in galaxies that are actively forming stars, the team, to its surprise, found that the FRBs tend to occur more often in massive star-forming galaxies than low-mass star-forming galaxies.

This alone was interesting because astronomers had previously thought that FRBs were going off in all types of active galaxies.

With this new information, the team started to ponder what the results revealed about fast radio bursts. Massive galaxies tend to be metal-rich because the metals in our universe—elements that are manufactured by stars—take time to build up over the course of cosmic history.

The fact that FRBs are more common in these metal-rich galaxies implies that the source of FRBs, magnetars, are also more common in these types of galaxies.

Stars that are rich in metals—which in astronomical terms means elements heavier than hydrogen and helium—tend to grow larger than other stars.

“A star with more metal content puffs up, drives mass transfer, culminating in a merger, thus forming an even more massive star with a total magnetic field greater than the individual star would have,” Sharma explained.

Future uses of the research

In the future, the team hopes to hunt down more fast radio bursts and their places of origin using DSA-110 and, eventually, the DSA-2000, an even bigger radio array planned to be built in the Nevada desert and completed in 2028.

Ravi concluded: “This result is a milestone for the whole DSA team. A lot of the authors of this paper helped build the DSA-110.

“The fact that the DSA-110 is so good at localising fast radio bursts bodes well for the success of DSA-2000.”

The European Southern Observatory (ESO) has revealed an insightful new image of a dark nebula that creates the illusion of a wolf-like silhouette against a colourful cosmic backdrop.

Fittingly nicknamed the Dark Wolf Nebula, it was captured in a 283-million-pixel image by the VLT Survey Telescope (VST) at ESO’s Paranal Observatory in Chile.

The dark nebula is located in the constellation Scorpius, near the centre of the Milky Way in the sky, approximately 5,300 light-years from Earth.

This image takes up an area in the sky equivalent to four full Moons but is actually part of an even larger nebula called Gum 55.

What are dark nebulae and why are they important?

Dark nebulae are cold clouds of cosmic dust so dense that they obscure the light of stars and other objects behind them.

As their name suggests, unlike other nebulae, they do not emit visible light. Dust grains within them absorb visible light and only let through radiation at longer wavelengths, like infrared light.

Astronomers study these clouds of frozen dust because they often contain new stars in the making.

This image shows in spectacular detail how the dark wolf stands out against the glowing star-forming clouds behind it.

The colourful clouds are built up mostly of hydrogen gas and glow in reddish tones, excited by the intense UV radiation from the newborn stars within them.

Mapping the southern sky in visible light

Some dark nebulae, like the Coalsack Nebula, can be seen with the naked eye –– and play a key role in how First Nations interpret the sky –– but not the Dark Wolf.

This image was created using data from the VLT Survey Telescope, which is owned by the National Institute for Astrophysics in Italy (INAF) and is hosted at ESO’s Paranal Observatory in Chile’s Atacama Desert.

The telescope has a specially designed camera to map the southern sky in visible light.

The picture was compiled from images taken at different times, each one with a filter letting in a different colour of light. They were all captured during the VST Photometric Hα Survey of the Southern Galactic Plane and Bulge (VPHAS+), which studied 500 million objects in our Milky Way.

Surveys like this help scientists to better understand the life cycle of stars within our home galaxy, and the obtained data are made publicly available through the ESO science portal.

Quasars are the most luminous objects in the Universe and are powered by material accreting onto supermassive black holes at the centres of galaxies.

Studies have shown that early-universe quasars have black holes so massive that they must have been swallowing gas at very high rates.

Most astronomers believe they formed in some of the densest environments in the universe where gas was most available.

However, observational measurements seeking to confirm this conclusion have so far yielded conflicting results.

Now, a new study using the Dark Energy Camera (DECam) points the way to an explanation for these disparate observations and a logical framework for connecting observation with theory.

Largest sky search of early-universe quasars

Utilising DECam’s massive field of view, the team conducted the largest on-sky area search ever around an early-universe quasar, trying to measure the density of its environment by counting the number of surrounding companion galaxies.

For their investigation, the team needed a quasar with a well-defined distance. Luckily, quasar VIK 2348–3054 has a known distance, determined by previous observations with the Atacama Large Millimeter/submillimeter Array (ALMA).

DECam’s three-square-degree field of view provided an expansive look at its cosmic neighbourhood.

Serendipitously, DECam is also equipped with a narrowband filter perfectly matched for detecting its companion galaxies.

“This quasar study really was the perfect storm,” said Trystan Lambert, who led the study. “We had a quasar with a well-known distance, and DECam on the Blanco telescope offered the massive field of view and exact filter that we needed.”

Using distance measurements to map neighbourhoods

DECam’s specialised filter allowed the team to count the number of companion galaxies around the early-universe quasar by detecting a very specific type of light they emit, known as Lyman-alpha radiation.

Lyman-alpha emitters are typically younger, smaller galaxies, and their Lyman-alpha emission can be used as a way to reliably measure their distances.

Distance measurements for multiple Lyman-alpha emitters can then be used to construct a 3D map of a quasar’s neighbourhood.

After systematically mapping the region of space around quasar VIK J2348-3054, Lambert and his team found 38 companion galaxies in the wider environment around the quasar — out to a distance of 60 million light-years — which is consistent with what is expected for quasars residing in dense regions.

However, they were surprised to find that within 15 million light-years of the quasar, there were no companions at all.

DECam’s role in offering new insights

This finding illuminates the reality of past studies aimed at classifying early-universe quasars and proposes a possible explanation for their conflicting results.

No other survey of this kind has used a search area as large as the one provided by DECam, so for smaller-area searches, a quasar’s environment can appear deceptively empty.

“DECam’s extremely wide view is necessary for studying quasar neighbourhoods thoroughly. You really have to open up to a larger area,” Lambert explained.

“This suggests a reasonable explanation as to why previous observations conflict with one another.”

Lambert’s team is currently following up with additional observations to obtain spectra and confirm star formation suppression.

They also plan to observe other quasars to build a more robust sample size.