Decoding the mysteries of the galaxy

Black holes nestled within glowing hydrogen shells. Photo: Anna de Graaff .

Astronomers have proposed a new theory about "black hole stars" to explain mysterious bright spots in the universe. These bright spots, called LRD (Little Red Dots), appeared very early in the history of the universe but their nature remains a mystery.

At first, scientists thought LRDs were old galaxies with lots of old stars. The reason is that their light looks like light from long-evolved stars. However, a team led by astrophysicist Anna de Graaff of the Max Planck Institute for Astronomy in Germany has challenged this based on observations of LRDs nicknamed The Cliff.

They argue that stars with such brightness could not have formed in the early Universe. “Instead, we propose that the most plausible model is an ionized luminous source, reddened by a dense, absorbing gas in the vicinity,” the team writes.

In other words, a thick layer of surrounding gas absorbed the light, turning it red. This resulted in a strong Balmer fault inside The Cliff, a signature used to determine the age of a star or galaxy, which many people mistakenly believe is too old. The Balmer fault is a signature in the spectrum that helps determine the age of a galaxy.

Young galaxies are made up of many O and B type stars that emit a lot of light at short wavelengths (blue, violet, ultraviolet). These stars only live a few million years, and when they die they create a sharp change in color, like a break in the spectrum. So the older the galaxy, the warmer its color becomes.

The Balmer fault of The Cliff is particularly large. Photo: Anna de Graaff.

Many LRDs show a strong Balmer rupture, which occurred just 600 million years after the Big Bang, 13.8 billion years ago. Scientists believe this is too early in the life of the universe for a galaxy to reach a state where older stars dominate.

This has led to a lot of research to understand what these “little red dots” in space actually are, while The Cliff presents a whole new challenge, with light that has traveled for 11.9 billion years, and the most pronounced Balmer fault ever recorded in an LRD.

“The extreme properties of The Cliff forced us to go back to the drawing board and build entirely new models,” de Graaff explains. With this strange feature in mind, the researchers developed a model of what they call a stellar black hole, a supermassive black hole actively swallowing matter from an accretion disk, surrounded and reddened by a dense shell of hydrogen rather than dust.

This structure somewhat resembles a star surrounded by superheated plasma. While regular stars shine thanks to internal fusion, black hole stars shine because the black hole swallows matter and heats the surrounding gas.

Currently, this hypothesis still needs more research to determine the existence and formation and evolution of black holes. However, Science Alert believes that this hypothesis is quite reasonable and will at least help to partly solve the problem of LRD while still maintaining the current understanding of humanity about the evolution of the universe.

“With its stringent constraints, such as its relatively modest redshift and high-quality spectroscopic and photometric observations, The Cliff becomes an ideal benchmark for future studies of active galactic nuclei and black hole stars,” the team writes.

Source: https://znews.vn/giai-ma-bi-an-ve-thien-ha-post1589001.html