(ORDO NEWS) — The stars live brightly, but the more they shine, the shorter their lifetime. Scientists tried to understand how many stellar “corpses” dot the cosmos and found something curious.
Everything dies in the end, even the brightest stars. In fact, the brightest stars are the ones with the shortest lives.
They consume all the hydrogen they have over a few million years and then explode in supernovae. The remains of their core collapse into a neutron star or black hole. These little dark objects dot our galaxy like a cosmic graveyard.
Both neutron stars and stellar black holes are difficult to detect. Neutron stars are only about fifteen kilometers in diameter, and unless their magnetic poles are aligned so that we see them as pulsars, they are usually overlooked.
Stellar black holes are even smaller and do not emit their own light. Some appear as microquasars when they consume the mass of a companion star, but most can only be seen when they pass between us and a more distant star, so they can be detected using microlensing.
Scientists have not yet observed enough of these stellar remnants to create an observable map of their general location, but a recent study in the Monthly Notices of the Royal Astronomical Society has modeled where we might find them.
What remains after the death of a star
The researchers studied the distribution of stars in our current galaxy and modeled how stellar remnants can be pulled and deflected by stellar interactions.
Since these “cemetery stars” are usually older than the current stars in the galaxy, they have had more time to move onto new orbital paths.
As you might expect, stellar remnants statistically experience some kind of blurring effect in their positions.
The distribution of these stars occurs in a plane three times thicker than that of the visible Milky Way. But the team found one aspect of their distribution that was rather unexpected.
About a third of these old dead stars are ejected from the galaxy. In their model, a third of the stars experienced a close stellar collision that gave them such a speed boost that they eventually escaped the Milky Way’s gravitational pull.
In other words, the ghosts leave the graveyard.
This means that over time the Milky Way “evaporates” or loses mass, which is unexpected.
We know that small clusters of stars, such as globular clusters, can evaporate, but the Milky Way is much more massive, so you might think that long-term evaporation would be minimal.
Another surprising aspect of the model is that these stellar remnants are fairly evenly distributed throughout the Milky Way. Most stars should have a stellar remnant within a hundred light years of them.
For the Sun, the most likely distance to the nearest stellar remnant is about 65 light-years. So a cosmic “ghost” can literally be in our backyard and we don’t even know it.
As more sky-surveying observatories, such as the Rubin Observatory, go online, researchers will look to catch microlensing events and discover where these stellar remnants really are. Then we can finally take a look at the galactic “dungeon” around us.
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