“In less than a hundred years, we have found a new way to think of ourselves,” observed Stephen Hawking. “From sitting at the center of the universe, we now find ourselves orbiting an average-sized sun, which is just one of billions of stars in our own Milky Way galaxy.” And now, a short-lived eclipse of an extremely bright x-ray source 23 million lightyears from Earth in the Whirlpool Galaxy, illuminated a world about the size of Saturn orbiting a binary star system –a stellar remnant, either a neutron star or black hole, and a massive star–further underscoring our cosmic insignificance.
Epic? –Discovery of M51-ULS-1b
This first potential planet, M51-ULS-1b, the ever to be found beyond our Milky Way, the galactic home to an estimated 40 billion alien worlds, was announced by a team led by Rosanne Di Stefano at the Harvard-Smithsonian Center for Astrophysics, who found the planet hunting through data from 2624 observations made by the Chandra X-ray Observatory space telescope. The Chandra measurements indicate that if the planet is real, it is a gas giant slightly smaller than Saturn, orbiting tens of astronomical units (AU) from the center of the binary system –at least as far from the system as Saturn is from the sun.
Milky Way’s Oldest Detected Planet
Flash back to October of 2017 –NASA’s Hubble Space Telescope measured the mass of the oldest known planet in our Milky Way galaxy near the core of the ancient globular star cluster M4, located 5,600 light-years away has an estimated age of 13 billion years, more than twice as old as Earth’s 4.5 billion years. Some of the oldest stars in the universe are found in ancient globular clusters that orbit around the Milky Way’s plane, the nucleus, which is circled by 150 globular clusters, harboring hundreds of thousands, and sometimes millions of stars, formed very early in the vast halo surrounding the embryonic Milky Way before it flattened to form the spiral disc that exists today.
The Milky Way’s oldest detected world, formed around a young, sun-like star barely 1 billion years after our universe’s birth in the Big Bang, orbits a peculiar pair of burned-out stars in the crowded core of a cluster of more than 100,000 stars.
Can Survive Longer than Current Age of the Universe
“A globular cluster might be the first place in which intelligent life is identified in our galaxy,” said DiStefano. “Once planets form, they can survive for long periods of time, even longer than the current age of the universe,” explained DiStefano.
Back to the new discovery, M51-ULS-1b, was detected by scanning the Chandra data for signs of transits, which occur when a planet blocks out the light when passing in front of a star or other bright object. To ensure that they only found real transits and not just fluctuations from the bright objects themselves, the researchers only looked for instances in which all of the light was blocked out.
“It’s exciting, but not unexpected,” says Angelle Tanner at Mississippi State University. “There’s absolutely no reason to think there wouldn’t be planets in other galaxies.” But not so fast says Matthew Kenworthy at Leiden University in the Netherlands. ““It’s sticky that there’s only one transit. The gold standard is three transits equally spaced from one another, because then you know it repeats.”
But if it’s more than a few AU out, says Kenworthy, “then it’s going to be decades before it comes around and causes a transit again,” he says. “I can’t think of a good way how I’d confirm this.”
The Chandra data opens new frontiers, similar to the discovery of the first exoplanet by Nobel-Prize laureates Michel Mayor and his colleague Didier Queloz, 51 Pegasi b a gaseous ball comparable with the solar system’s biggest gas giant, Jupiter, in October, 1995 at the Haute-Provence Observatory in southern France, using custom-made instruments. Their discovery opened a new era in humanity’s exploration of our galactic neighborhood and forever changed our view of the cosmos. Since then over 4,000 exoplanets have been found in our home galaxy.
The 51 Pegasi b discovery, foreshadowing M51-ULS-1b, opens a very old question which was debated by philosophers says Mayor: “are there other worlds in the Universe?,” Mayor said. “We don’t know!” he added, “The only way to do it is to develop techniques that would allow us to detect life at a distance.”
Image credit: The Whirlpool galaxy in a new visualization that combines observations from the Hubble and Spitzer space telescopes and Chandra X-ray Observatory. (Image credit: Visualization: F. Summers, J. DePaxquale, D. Player (STScI), K. Arcand (SAO/CXC), R. Hurt (Caltech/IPAC)