“I see your glory as a shooting star.”
This is what the Earl of Salisbury says as he ruminates on the future in Shakespeare’s “Richard II”.
During the English Renaissance, people believed that shooting stars were luminaries falling from the sky and warning signs of calamity. But at the end of the 19th century, scientists had established the truth is much more banal. What is commonly called today shooting or shooting stars are simply small pieces of rock or dust that burn quickly upon entering Earth’s atmosphere.
But nature has a surprise in store for you: shooting stars do exist.
From 2005 to 2014, a monumental observation program incorporating the Sloan Digital Sky Poll and telescopes at Fred Lawrence Whipple Observatory have confirmed a new class of stars that move at such incredible speed that they can escape the gravity of their home galaxies.
Astronomers are only just beginning to understand these actual shooting stars – called hypervelocity stars – which roam the cosmos at millions of miles per hour.
Shooting stars and slingshot
The history of hypervelocity stars begins in 1988, when Jack Gilbert Hills, theorist of Los Alamos National Laboratories, had an inspired idea: what if a binary star system – i.e. two stars that are gravitationally related to each other and orbit around a common center of mass – was traveling near the massive black hole in the center of the Milky Way? Calculated hills that the tidal force black hole could tear the binary system in half.
Imagine two skaters holding hands and spinning around until they suddenly let go. The two skaters will fly away from each other. Likewise, when two stars in a binary system are torn apart by a close encounter with a black hole, they fly away. In such an encounter, a star could gain enough energy to be completely expelled from the galaxy.
Astronomers now know that this is how hyperspeed stars are born.
Theory, observations and simulations
Following the publication of Hills’ premonitory article, the astronomical community viewed hypervelocity stars as an intriguing possibility, albeit without evidence of observation. This changed in 2005.
By observing the stars in the Milky Way Halo, a team of researchers using the MMT Observatory in Arizona came across something very unexpected. They observed a star escaping the Milky Way at nearly 3.2 million km / h. It was HVS1, the first known hypervelocity star.
The sightings tell part of the story, but to help answer other questions – like what happens to the mate after they separate from the hyperspeed star – my advisor and I turned to computer simulations. Our models predict that the other star of the first pair is often left in orbit around the black hole much the same way the Earth revolves around the Sun.
Another exciting result of these modeling efforts has been the discovery that sometimes the two stars can crash. When this happens, the stars can merge into a very massive star.
If you’re wondering what could happen to a planet orbiting one of these stars, we’ve modeled that as well. In one short article from 2012, my colleagues and I have shown that the black hole at the center of our galaxy can detonate planets outside the Milky Way at nearly 5% the speed of light.
To date, no hyperspeed planet has been detected, but they could very well be there, waiting for some happy astronomers to stumble upon them.
All the fast stars don’t leave the galaxy
Using data from Gaia Spaceship, launched in 2013, my colleagues and I discovered that some of the stars that the astronomical community previously considered to be “hyperspeed stars” are in fact probably related to the Milky Way galaxy.
While this result may seem disappointing, it actually reveals two critical points. First, there are different mechanisms for accelerating stars to high speeds. Today, astronomers know thousands of fast stars. However, just because a star is moving fast does not necessarily make it a hyperspeed star unrelated to the Milky Way. Second, the true hyperspeed stars escaping the Milky Way may be rarer than previously thought.
The future is bright and fast
I find it beautiful that real shooting stars exist. Equally amazing is that studying their trajectories and speeds can help answer some of the most important questions in science today.
For example, hypervelocity stars might offer clues about the nature and distribution of dark matter In the universe. Hypervelocity stars may also be the key to responding if there is more than one black hole at the center of the galaxy.
My students use NASA Satellite for the study of exoplanets in transit to search for planets around these blazingly fast stars. The discovery of a single planet around a hypervelocity star will forever change ideas about planetary formation and survivability.
These stars are fast, but slowly they shed light on the secrets of nature. While you might not be able to see a real shooting star with your own eyes, you can certainly wish you could.
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