Andromeda Galaxy (Space & Defence Sectors)
Andromeda Galaxy (Space & Defence Sectors)
Why In News:
A new Hubble Space Telescope study, published on 27 July 2026, shows that star formation in the Andromeda Galaxy (M31) has collapsed by about 80% over the last 500 million years, placing our nearest large galactic neighbour in a transitional 'green valley' stage between active star formation and complete quiescence.
Source: The Hindu, Page 18, 29 July 2026 - 'Andromeda: galactic middle age'
Andromeda Galaxy
The Andromeda Galaxy, also catalogued as M31 (NGC 224), is the nearest large spiral galaxy to the Milky Way, located about 2.5 million light-years away in the constellation Andromeda.
It is one of the few galaxies visible to the naked eye from Earth, appearing as a faint smudge of light.
The new Hubble study reveals that its star-formation rate has dropped from about 1 solar mass per year to around 0.2 solar masses per year.
Astronomers describe Andromeda as being in the 'green valley', a transitional phase between 'blue' star-forming galaxies and 'red' quiescent (quenched) galaxies.
A compact satellite galaxy called M32 is believed to have contributed to suppressed star formation in parts of Andromeda's disc, beginning roughly 60 million years ago.
Key Facts for Prelims
The study was conducted as part of the broader PHAT/PHAST (Panchromatic Hubble Andromeda Treasury) survey programme, which has imaged large portions of Andromeda's disc over the past decade.
Various Types of Galaxies
Spiral galaxies are characterised by a flattened, rotating disk that contains spiral arms where active star formation takes place, along with a central bulge.
These galaxies can be either barred or unbarred in structure. Prominent examples include the Milky Way and the Andromeda Galaxy.
Elliptical galaxies have a smooth, oval or nearly spherical shape and contain very little gas and dust, which results in minimal new star formation.
They are primarily composed of older stars. A well-known example is Messier 87.
Lenticular galaxies are considered intermediate between spiral and elliptical galaxies.
They possess a disk-like structure similar to spiral galaxies but lack distinct spiral arms, making them appear smoother. An example is the Sombrero Galaxy.
Active galaxies are galaxies that emit significantly more energy-often up to 100 times more-from their central regions than can be explained by their stars alone.
This excess energy is powered by a supermassive black hole at the core.