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“The imagination will often transport us to worlds that never have been. But without that, we’re not going anywhere, ”said Carl Sagan. So imagine a galaxy filled with tens of millions of black holes and dark, lifeless island worlds – planets floating, unmoored to gravity and the life-giving light of an alien star. It is now increasingly clear that the Milky Way can be such a galaxy. An upcoming NASA mission may find there are more rogue planets – planets that float in space without orbiting a sun – than there are stars in the Milky Way, theorizes a new study.
“It gives us a window into these worlds that we wouldn’t have otherwise,” said Samson Johnson, of Ohio State University and lead author of the study. “Imagine our little rocky planet floating freely in space – that’s what this mission will help us find.”
The Roman telescope
The study calculated that NASA’s upcoming Nancy Grace Roman Space Telescope could find hundreds of rogue planets in the Milky Way. Identifying these planets, Johnson said, will help scientists deduce the total number of rogue planets in our galaxy. Rogue or floating planets are isolated objects that have masses similar to planets. The origin of these objects is unknown, but one possibility is that they were previously linked to a host star.
“The invisible galaxy” – 100 million black holes hidden in the Milky Way
“The universe could be teeming with rogue planets and we wouldn’t even know it,” said Scott Gaudi, distinguished astronomy professor and scholar at Ohio State and co-author of the article. “We would never know without undertaking an in-depth study of the space microlens as Roman will do.”
The Roman telescope, named after NASA’s first chief astronomer, also known as the “mother” of the Hubble Telescope, will attempt to build the first census of rogue planets, which could, Johnson said, help scientists understand how these planets are forming. Roman will also have other goals, including finding planets that orbit the stars in our galaxy.
This process is not well understood, although astronomers know it is complicated. Rogue planets could form in the gas disks around young stars, similar to those planets still linked to their host stars. After their formation, they could later be ejected by interactions with other planets in the system, or even by events overflown by other stars. Or they could form when dust and gas swirl together, like stars form.
The Roman telescope, Johnson said, is designed not only to locate planets floating in the Milky Way, but to test the theories and models that predict the formation of these planets.
Research will span 24,000 light years from the Milky Way
Johnson’s study found that this mission is probably 10 times more sensitive to these objects than existing efforts, which for now are based on telescopes attached to the Earth’s surface. It will focus on the planets of the Milky Way, between our sun and the center of our galaxy, spanning some 24,000 light years.
“Several rogue planets have been discovered, but to get the full picture our best bet is something like Roman,” he says. “It’s a totally new frontier.”
The mission, which is slated to launch in the next five years, will search for rogue planets using a technique called a gravitational microlens. This technique relies on the gravity of stars and planets to bend and magnify light from stars passing behind them from the telescope’s point of view.
This illustration shows a rogue planet drifting through the galaxy alone. Credit: NASA / JPL-Caltech / R. Injured (Caltech-IPAC)
Gravitational Microlensification – Einstein’s General Relativity
This microlensing effect is linked to Albert Einstein’s general theory of relativity and allows a telescope to find planets thousands of light years from Earth – much further than other planet-detecting techniques. BBecause the microlens only work when the gravity of one planet or star bends and amplifies the light of another star, the effect of a given planet or star is only visible for a short period once every few million years. And since rogue planets are located in space on their own, with no stars nearby, the telescope must be very sensitive to detect this magnification.
The study estimates that this mission will be able to identify rogue planets of the mass of Mars or more. Mars is the second smallest planet in our solar system and is just over half the size of Earth.
Johnson said these planets are unlikely to support life. “They would probably be extremely cold because they don’t have a star,” he says. (Other research missions involving astronomers from the state of Ohio will look for exoplanets that may harbor life.) SStudying them will help scientists better understand how all planets form, he said.
“If we find a lot of low-mass rogue planets, we’ll know that when stars form planets, they probably eject a bunch of other things into the galaxy,” he says. “It helps us get an idea of the formation path of planets in general. Up to six billion Earth-like planets in our galaxy, new estimates show
Source: Samson A. Johnson et al. Predictions from the investigation of galactic exoplanets from the Nancy Grace Roman Space Telescope. II. Detection rate of free floating planets, The Astronomical Journal (2020). DOI: 10.3847 / 1538-3881 / aba75b, iopscience.iop.org/article/10. … 847 / 1538-3881 / aba75b
The Daily Galaxy, Sam Cabot, via Ohio State University
Image credits: NASA
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