Astronomy Now Home
Home Magazine Resources Store

On Sale Now!



The October 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). Astronomy Now is the only astronomy magazine specially designed to be read on tablets and phones. Download the app from Google Play Store or the Apple App Store.



Top Stories



Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...
  READ MORE

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...
  READ MORE

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...
  READ MORE








Dead galaxies
show signs of life

By James Lloyd
for ASTRONOMY NOW
Posted: 01 June 2011


Bookmark and Share

Using the Hubble Space Telescope, astronomers at the University of Michigan have discovered star formation in old, ‘dead’ galaxies, providing new insights into galaxy evolution.

Alyson Ford and Joel Bregman spotted this stellar activity in four galaxies situated 40 million light years away from us. "We have directly detected individual young stars and star clusters in galaxies that were thought to have ceased forming stars a very long time ago," says Ford, who presents the results this week at a Canadian Astronomical Society meeting in London, Ontario. "Finding this evidence for low levels of ongoing star formation in these ‘dead’ galaxies was quite surprising."


Messier 105, seen in the top, left corner in an image from the Sloan Digital Sky Survey. The outlined region in the centre of Messier 105 is expanded to reveal Hubble's unique view of the galaxy's inner region, which is further expanded to unveil several individual young stars and star clusters (denoted by dashed circles; top, right). Image: H. Alyson Ford and Joel N. Bregman (University of Michigan).

Ford and Bregman studied elliptical galaxies, mostly composed of older, low-mass stars. Unlike spiral galaxies, such as our own Milky Way, elliptical galaxies have no disc of cold, dense gas from which new stars can be regularly formed.

Star formation in these galaxies was thus considered to be non-existent. This is supported by their observed colours: elliptical galaxies tend to have a yellow-red hue, whereas typical spiral galaxies have a blue glow emanating from their young, hot stars.

In this study, the astronomers used the Wide Field Camera 3 aboard the Hubble Space Telescope to make detailed ultraviolet images of the galaxies, allowing them to pick out individual stars that were previously unresolved.

The breakthrough came when observing Messier 105, an elliptical galaxy in the constellation Leo. Ford and Bregman noticed a handful of very bright, blue stars – the first hints of star formation in this galaxy.

They also detected objects that weren’t blue enough to be single stars. "We were confused by some of the colours of objects in our images until we realised that they must be star clusters,” explains Ford. This star formation represents a continuous process, rather than a burst of activity, in which stars form at an average rate of one Sun every 10,000 years.

Jaymie Matthews, an astronomer at the University of British Columbia, Canada, who was not involved in this study, is excited about these findings. “We astronomers bought into the textbook stereotypes of galaxy classification,” says Matthews. “[This study] will force us to stop and think more carefully about the chemical and dynamical evolution of elliptical galaxies.”

So what mechanisms could be responsible for this mysterious star formation in elliptical galaxies? Ford and Bregman have no answer yet, but hope that further work may provide some hints. “We're hoping to make more observations of other nearby elliptical galaxies to gain further insight into the star formation process, including any clues that can help us determine the history of the gas that these new stars are forming from,” says Ford.

Meanwhile, Jaymie Matthews has come up with a novel analogy for galaxy classification: “Spiral galaxies: lots of gas, many stars being born; the galactic equivalent of Los Angeles. Elliptical galaxies: no gas, only old geezers with all the bright lights long ago extinguished; the galactic equivalent of a Perry Como Fan Club meeting in a Prius factory. But like humans and societies, if you look closely enough, the stereotypes fall apart as they are far too simplistic and unfair.”

The moral of the story, then? “Never judge a galaxy by its colour.”

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.
 GET YOUR COPY

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
 GET YOUR COPY

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
 GET YOUR COPY


HOME | NEWS ARCHIVE | MAGAZINE | SOLAR SYSTEM | SKY CHART | RESOURCES | STORE | SPACEFLIGHT NOW

© 2014 Pole Star Publications Ltd.