The Milky Way-like galaxy NGC 1232 (center) shows the Milky Way's
location and relative size. Images of dwarf galaxies are centered close
to their true locations but have been magnified for visibility. Credit:
Charlotte Olsen. Hi-res image
Three dozen dwarf galaxies far
from each other had a simultaneous “baby boom” of new stars, an
unexpected discovery that challenges current theories on how galaxies
grow and may enhance our understanding of the universe.
Galaxies more than 1 million light-years apart should have completely
independent lives in terms of when they give birth to new stars. But
galaxies separated by up to 13 million light-years slowed down and then
simultaneously accelerated their birth rate of stars, according to a
Rutgers-led study published in the Astrophysical Journal.
“It appears that these galaxies are responding to a large-scale change
in their environment in the same way a good economy can spur a baby
boom,” said lead author Charlotte Olsen, a doctoral student in the Department of Physics and Astronomy in the School of Arts and Sciences at Rutgers University–New Brunswick.
“We found that regardless of whether these galaxies were next-door
neighbors or not, they stopped and then started forming new stars at the
same time, as if they’d all influenced each other through some
extra-galactic social network,” said co-author Eric Gawiser, a professor in the Department of Physics and Astronomy.
The simultaneous decrease in the stellar birth rate in the 36 dwarf
galaxies began 6 billion years ago, and the increase began 3 billion
years ago. Understanding how galaxies evolve requires untangling the
many processes that affect them over their lifetimes (billions of
years). Star formation is one of the most fundamental processes. The
stellar birth rate can increase when galaxies collide or interact, and
galaxies can stop making new stars if the gas (mostly hydrogen) that
makes stars is lost.
Star formation histories can paint a rich record of environmental
conditions as a galaxy “grew up.” Dwarf galaxies are the most common but
least massive type of galaxies in the universe, and they are especially
sensitive to the effects of their surrounding environment.
The 36 dwarf galaxies included a diverse array of environments at
distances as far as 13 million light-years from the Milky Way. The
environmental change the galaxies apparently responded to must be
something that distributes fuel for galaxies very far apart. That could
mean encountering a huge cloud of gas, for example, or a phenomenon in
the universe we don’t yet know about, according to Olsen.
The scientists used two methods to compare star formation histories. One
uses light from individual stars within galaxies; the other uses the
light of a whole galaxy, including a broad range of colors.
“The full impact of the discovery is not yet known as it remains to be
seen how much our current models of galaxy growth need to be modified to
understand this surprise,” Gawiser said. “If the result cannot be
explained within our current understanding of cosmology, that would be a
huge implication, but we have to give the theorists a chance to read
our paper and respond with their own research advances.”
“The James Webb Space Telescope, scheduled to be launched by NASA this
October, will be the ideal way to add that new data to find out just how
far outwards from the Milky Way this ‘baby boom’ extended,” Olsen
added.
Rutgers co-authors include Professor Kristen B. W. McQuinn; Grace Telford, a postdoctoral associate; and Adam Broussard, a doctoral student. Scientists at the University of Toronto, the Harvard-Smithsonian Center for Astrophysics, Johns Hopkins University and NASA’s Goddard Space Flight Center contributed to the study.
Media Contact:
John Cramer
jdc268@echo.rutgers.edu
Source: Rutgers - The State University of New Jerse/News
