According to a new study from researchers from Harvard and the Tata Institute of Fundamental Research (Mumbai), scientists looking for extraterrestrial life may have been looking mainly in the wrong places to date. Most astronomers have written off the chances of finding extraterrestrial civilizations in globular clusters, some of which serve as home to millions of stars because only one of the thousands of known extrasolar planets occurs in these dense star clusters. Moreover, the current prevailing theory is that gravitational interactions among the closely packed stars would have ended up eventually flinging most planets out of the solar systems into deep space.
New research, however, casts doubt on the current theory about globular clusters. It turns out that the proximity of all those stars could actually be an advantage in supporting life, explains Rosanne DiStefano, a theoretical astrophysicist at the Harvard-Smithsonian Center for Astrophysics. She argues that he relative proximity of stars also means that lots of planetary systems are not very far from one another. “If there is an advanced society in an environment like that, it could set up outposts relatively easily, because we’re dealing with distances that are so much shorter,” she points out.
Moreover, closely-knit civilizations in a globular cluster might last for a very long time, and therefore more likely to be around to interact with humans now or in the future.
DiStefano authored the paper with Alak Ray of the Tata Institute of Fundamental Research on Wednesday, January 6th at an American Astronomical Society meeting in Florida. The paper was published in the most recent edition of the academic journal Nature.
More on dense star clusters as ideal for extraterrestrial life
The first thing to keep in mind is that Milky Way has close to 150 globular clusters, and these dense star clusters contain some of the oldest known stars, in some cases up to 10 billion years or longer.
“It’s premature to say there are no planets in globular clusters,” Ray commented in a recent interview.
DiStefano and Ray also question the theory that a neighboring star is likely to come too close and disrupt a planetary system, possibly sending planets into interstellar space.
The study authors argue that a star’s habitable zone (the distance at which a planet would be warm enough for liquid water) varies based on the star. That means brighter stars have more distant habitable zones, and planets orbiting dimmer stars would have to be much closer to be habitable. Brighter stars “live” less long, and since globular clusters are quite old, many of these stars have died out. The main s stars in globular clusters today are long-lived red dwarfs. Any habitable planets they host must be close in and less likely to suffer a catastrophic event from stellar interactions.
DiStefano notes: “Once planets form, they can survive for long periods of time, even longer than the current age of the universe,”
If habitable planets can form in dense star clusters and survive for billions of years, that means life would have time to develop and become complex, or even develop intelligence.
Also keep in mind that any civilization that did develop would do so in a much different environment. The nearest star to our solar system is four light-years (24 trillion miles) away. The nearest star in a globular star cluster would probably be 20 times closer, around one trillion miles away. The researchers suggest this proximity would make interstellar communication and exploration much easier.
“We call it the ‘globular cluster opportunity,'” explains DiStefano. “Sending a broadcast between the stars wouldn’t take any longer than a letter from the U.S. to Europe in the 18th century.”
She continued to note that “Interstellar travel would take less time too. The Voyager probes are 100 billion miles from Earth, or one-tenth as far as it would take to reach the closest star if we lived in a globular cluster. That means sending an interstellar probe is something a civilization at our technological level could do in a globular cluster.”