ESO’s Very Large Telescope (VLT) has observed the central part of the Milky Way with spectacular resolution and uncovered new details about the history of star birth in our galaxy. Thanks to the new observations, astronomers have found evidence for a dramatic event in the life of the Milky Way: a burst of star formation so intense that it resulted in over a hundred thousand supernova explosions. ...
In the study ... the team found that about 80% of the stars in the Milky Way central region formed in the earliest years of our galaxy, between eight and 13.5 billion years ago. This initial period of star formation was followed by about six billion years during which very few stars were born. This was brought to an end by an intense burst of star formation around one billion years ago when, over a period of less than 100 million years, stars with a combined mass possibly as high as a few tens of million Suns formed in this central region.
GALACTICNUCLEUS: A High Angular Resolution JHKs Imaging Survey of the Galactic Centre:
II. First Data Release of the Catalogue and the Most Detailed CMDs of the GC ~ F. Nogueras-Lara et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk. — Garrison Keillor
ESO’s Very Large Telescope (VLT) has observed the central part of the Milky Way with spectacular resolution and uncovered new details about the history of star birth in our galaxy. Thanks to the new observations, astronomers have found evidence for a dramatic event in the life of the Milky Way: a burst of star formation so intense that it resulted in over a hundred thousand supernova explosions. ...
In the study ... the team found that about 80% of the stars in the Milky Way central region formed in the earliest years of our galaxy, between eight and 13.5 billion years ago. This initial period of star formation was followed by about six billion years during which very few stars were born. This was brought to an end by an intense burst of star formation around one billion years ago when, over a period of less than 100 million years, stars with a combined mass possibly as high as a few tens of million Suns formed in this central region.
I find this research incredibly fascinating, but I wondered how astronomers could tell the difference between stars that are 1 billion years old and those that are 8 billion years old. Whether 1 billion years old or 8 billion years old, all these stars look "old and red".
The answer is that the astronomers looked for "red clump stars". They found two distinctive red clumps near the galactic center. Almost certainly, the 1 Gyr clump must have been considerably brighter than the 8 Gyr clump, because the younger clump must be made up of relatively massive stars, which must have been lost long ago in the stellar population forming the older clump.
Huge gamma ray bubbles of the Milky Way.
Credit: NASA's Goddard Space Flight Center
Isn't it possible that the enormous starburst that took place one billion years ago in the center of the Milky Way may have had something to do with the two enormous gamma ray bubbles that extend 25,000 light years above and below the plane of the Milky Way?
Isn't it possible that the enormous starburst that took place one billion years ago in the center of the Milky Way may have had something to do with the two enormous gamma ray bubbles that extend 25,000 light years above and below the plane of the Milky Way?
Unveiling the Origin of the Fermi Bubbles
by H.-Y. Karen Yang* , Mateusz Ruszkowski and Ellen G. Zweibel
The Fermi bubbles are two giant bubbles extending ∼50º above and below the Galactic Center (GC) revealed by the Fermi Gamma-ray Space Telescope. They are one of the three elephants in the gamma-ray sky (among Loop I and the Galactic Center Excess): the solid angle of the bubbles is about 1 sr, which is roughly that of an elephant standing in a room. They are “elephants in the room” also because of their mysterious physical origin. Their symmetry about the GC suggests that they originate from powerful energy injections from the GC, possibly related to nuclear star formation (NSF) or active galactic nucleus (AGN) activity.
3.1. General Considerations
In terms of understanding the physical origin of the Fermi bubbles, three major questions need to be addressed. First, what is the emission mechanism? The bubbles can either be hadronic, where the gamma rays are produced by inelastic collisions between CRp and the thermal nuclei via decay of neutral pions, or leptonic, where the gamma rays are generated by inverse-Compton (IC) scattering of the interstellar radiation field (ISRF) by CR electrons (CRe). Second, what activity at the GC triggered the event—are the bubble associated with NSF or AGN activity? Third, where are the CRs accelerated? They could either be accelerated at the GC and transported to the surface of the bubbles, or accelerated in situ by shocks or turbulence.
Note, however, that not all combinations of the above three considerations would make a successful model because of constraints given by the hard spectrum of the observed bubbles. For instance, if the bubbles are leptonic, the synchrotron and IC cooling time of high-energy (∼TeV) CRe gives a very stringent age limit on the bubbles to be within a few million years old.>>
