Question

2) What is the concept of multiple star forming generations? How does this process work? What can you conclude about planets in a newly formed galaxy?

Answer 1

You can get a detailed idea in the paper 1012.3294 in arxive.

for second question

Using information from NASA's Chandra X-ray Observatory and a planet detection technique called microlensing to study a distant quasar galaxy , scientists at the University of Oklahoma found evidence that there are approximately 2,000 extragalactic planets for every one star beyond the Milky Way. Some of these exoplanets are as (relatively) small as the moon, while others are as massive as Jupiter. Unlike Earth, most of the exoplanets are not tightly bound to stars, so they're actually wandering through space or loosely orbiting between stars.We can estimate that the number of planets in this [faraway] galaxy is more than a trillion," says Xinyu Dai, the astronomy and astrophysics professor who led the study.

View Images

Milky Way from Cerro Paranal observatory in the Atacama Desert, Chile.
Photograph by Babak Tafreshi, National Geographic Creative

By Elaina Zachos

PUBLISHED February 5, 2018

Scientists have long been unable to find exoplanets—planets outside the solar system—beyond the confines of the Milky Way. After all, our galaxy is a warped disc about a hundred thousand light-years across and a thousand light-years thick, so it's incredibly difficult to see beyond that. But now, a new study is saying there could be extragalactic exoplanets.

The study, published February 2 in The Astrophysical Journal Letters, gives the first evidence that more than a trillion exoplanets could exist beyond the Milky Way.

Beyond Our Galaxy

Using information from NASA's Chandra X-ray Observatory and a planet detection technique called microlensing to study a distant quasar galaxy , scientists at the University of Oklahoma found evidence that there are approximately 2,000 extragalactic planets for every one star beyond the Milky Way. Some of these exoplanets are as (relatively) small as the moon, while others are as massive as Jupiter. Unlike Earth, most of the exoplanets are not tightly bound to stars, so they're actually wandering through space or loosely orbiting between stars.

"We can estimate that the number of planets in this [faraway] galaxy is more than a trillion," says Xinyu Dai, the astronomy and astrophysics professor who led the study.

View Images

A microlensing image highlights possible exoplanets beyond the Milky Way.

Courtesy of the University of Oklahoma

Microlensing works like magnification, says co-author Eduardo Guerras. It's a highly nuanced process that looks at frequencies emitted by moving celestial objects, meant to observe how they distort and magnify light that comes in from the objects near them. This light then illuminates things that aren't otherwise visible.

"This microlensing is amplifying something that is very small and changing colors, which makes no sense," Guerras says, "or it's amplifying a small region of a bigger object and that object has different colors."

Since these objects are so distant—the extragalactic bodies are some 3.8 billion years away—microlensing is the only way to get a sense of their shape. The researchers know they're looking at planets because of the speed at which they're moving.

"You can have this effect with stars, but it would be much, much less likely. It would be way less frequent," Guerras says. "If you have only one planet, the chances of observing it twice is astronomically small."