Little Mohamed Western

Scientists have recently discovered a new class of small, very hot pulsars that change their brightness every few minutes. This type of star, called "semi-dwarf pulsars", is thought to have originated from the interruption of the life cycle known to large stars.

Analyzing data from an astronomical survey launched in 2018 from the Palomar Observatory in California, scientists found four of these hot semi-dwarf pulsars.

These stars pulsate at intervals of 200 to 475 seconds, while their brightness varies by about 5%.

However, this change in brightness can theoretically be produced by blocking for binary stars. But scientists have ruled out this possibility, realizing that they have found a new class of stars called "semi-dwarf B-stars."

What are the characteristics of these strange stars?
"There are many stars pulsing, including our sun, but they do it on a very small scale," says physicist Thomas Kopfer of the University of California-Santa Barbara's Cavley Institute of Theoretical Physics.

"Stars with large variations in brightness are usually radiant - and seem to breathe - while their sizes change completely," the lead author of the study says.

Although our sun beats, the cycle of each pulse is 11 years, and its brightness changes only by 0.1% throughout this period, while the difference in the brightness of some pulsars 10% due to changes in size and temperature, so the sun is not classified in this category Who are the stars.

The "dwarf-b stars" are of interest to scientists because they are very small, perhaps up to 10% of the size of the sun, but they are also very dense.

The star's mass in this small diameter can be between 20 and 50% of the Sun's mass.

The premature star
As a result of this density, its nuclear furnace in its center produces a huge amount of energy by converting helium into carbon and oxygen, which makes it very bright, and tends to blue while the temperature on its surface ranges between twenty thousand and forty thousand degrees Kelvin (between four and eight times the temperature of the surface of the sun).

Scientists believe that this type of stars arise after the explosion of primary stars up to eight times the mass of the sun.

When these stars run out of hydrogen in their center after being transformed into helium through fusion nuclear reactions, new nuclear reactions start turning helium into carbon and oxygen, and the star turns into a red giant.

A semi-dwarf B-star arises as a mother receives her baby prematurely, when the outer hydrogen layers separate from the red giant before helium melts, possibly due to the influence of a binary companion, but the exact mechanisms of how this occurs are unknown.

Researchers are still looking at the exact mechanism behind the oscillations of hot semi-dwarf pulsars, but believe they may be unstable radiation patterns caused by the accumulation of iron in the star leading to the formation of an energy layer that leads to the pulse.

Scientists also believe that another difference may have occurred in the center of the star. While "dwarf-b stars" melt helium in or around the nucleus, scientists believe that hot semi-dwarf pulsars lost their outer layers before helium was hot and dense enough to start melting.

The next step will be to further clarify what is actually happening within these stars to produce pulses, and to determine where the stars fit precisely with the stellar evolution models that scientists know.