Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Giant galaxy is still growing

25.06.2015

Messier 87 has swallowed an entire galaxy in the last billion years

Astronomers expect that galaxies grow by swallowing smaller galaxies. But the evidence is usually not easy to see -- just as the remains of the water thrown from a glass into a pond will quickly merge with the pond water, the stars in the infalling galaxy merge in with the very similar stars of the bigger galaxy leaving no trace.


The huge halo around giant elliptical galaxy Messier 87 appears on this very deep image. An excess of light in the top-right part of this halo, and the motion of planetary nebulae in the galaxy, are the last remaining signs of a medium-sized galaxy that recently collided with Messier 87. The image also reveals many other galaxies forming the Virgo Cluster, of which Messier 87 is the largest member. In particular, the two galaxies at the top right of the frame are nicknamed 'the Eyes'.

Credit: Chris Mihos (Case Western Reserve University)/ESO

But now a team of astronomers led by PhD student Alessia Longobardi at the Max-Planck-Institut für extraterrestrische Physik , Garching, Germany has applied a clever observational trick to clearly show that the nearby giant elliptical galaxy Messier 87 merged with a smaller spiral galaxy in the last billion years.

"This result shows directly that large, luminous structures in the Universe are still growing in a substantial way -- galaxies are not finished yet!" says Alessia Longobardi. "A large sector of Messier 87's outer halo now appears twice as bright as it would if the collision had not taken place."

Messier 87 lies at the centre of the Virgo Cluster of galaxies. It is a vast ball of stars with a total mass more than a million million times that of the Sun, lying about 50 million light-years away.

Rather than try to look at all the stars in Messier 87 -- there are literally billions and they are too faint and numerous be studied individually -- the team looked at planetary nebulae, the glowing shells around ageing stars [1]. Because these objects shine very brightly in a specific hue of aquamarine green, they can be distinguished from the surrounding stars. Careful observation of the light from the nebulae using a powerful spectrograph can also reveal their motions [2].

Just as the water from a glass is not visible once thrown into the pond -- but may have caused ripples and other disturbances that can be seen if there are particles of mud in the water -- the motions of the planetary nebulae, measured using the FLAMES spectrograph on the Very Large Telescope , provide clues to the past merger.

"We are witnessing a single recent accretion event where a medium-sized galaxy fell through the centre of Messier 87, and as a consequence of the enormous gravitational tidal forces, its stars are now scattered over a region that is 100 times larger than the original galaxy!" adds Ortwin Gerhard, head of the dynamics group at the Max-Planck-Institut für extraterrestrische Physik, Garching, Germany, and a co-author of the new study.

The team also looked very carefully at the light distribution in the outer parts of Messier 87 and found evidence of extra light coming from the stars in the galaxy that had been pulled in and disrupted. These observations have also shown that the disrupted galaxy has added younger, bluer stars to Messier 87, and so it was probably a star-forming spiral galaxy before its merger.

"It is very exciting to be able to identify stars that have been scattered around hundreds of thousands of light-years in the halo of this galaxy -- but still to be able to see from their velocities that they belong to a common structure. The green planetary nebulae are the needles in a haystack of golden stars. But these rare needles hold the clues to what happened to the stars," concludes co-author Magda Arnaboldi (ESO, Garching, Germany).

###

Notes

[1] Planetary nebulae form as Sun-like stars reach the ends of their lives, and they emit a large fraction of their energy in just a few spectral lines, the brightest of which is in the green part of the spectrum. Because of this, they are the only single stars whose motions can be measured at Messier 87's distance of 50 million light-years from Earth. They behave like beacons of green light and as such they tell us where they are and at what velocity they are travelling.

[2] These planetary nebulae are still very faint and need the full power of the Very Large Telescope to study them: the light emitted by a typical planetary nebula in the halo of the Messier 87 galaxy is equivalent to two 60-watt light bulbs on Venus as seen from Earth.

The motions of the planetary nebulae along the line of sight towards or away from Earth lead to shifts in the spectral lines, as a result of the Doppler effect. These shifts can be measured accurately using a sensitive spectrograph and the velocity of the nebulae deduced.

More information

This research was presented in a paper entitled "The build-up of the cD halo of M87 -- evidence for accretion in the last Gyr", by A. Longobardi et al., to appear in the journal Astronomy & Astrophysics Letters on 25 June 2015.

This work was also presented at the annual conference of the European Astronomical Society, EWASS 2015 , which is being held in La Laguna, Tenerife, at the same time.

The team is composed of A. Longobardi (Max-Planck-Institut für extraterrestrische Physik, Garching, Germany), M. Arnaboldi (ESO, Garching, Germany), O. Gerhard (Max-Planck-Institut für extraterrestrische Physik, Garching, Germany) and J.C. Mihos (Case Western University, Cleveland, Ohio, USA).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world's most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world's largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

Links

Contacts

Alessia Longobardi
Max-Planck-Institut für extraterrestrische Physik
Garching bei München, Germany
Tel: +49 89 30000 3022
Email: alongobardi@mpe.mpg.de

Magda Arnaboldi
ESO
Garching bei München, Germany
Tel: +49 89 3200 6599
Email: marnabol@eso.org

Ortwin Gerhard
Max-Planck-Institut für extraterrestrische Physik
Garching bei München, Germany
Tel: +49 89 30000 3539
Email: gerhard@mpe.mpg.de

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org

http://www.eso.org 

Richard Hook | EurekAlert!

More articles from Physics and Astronomy:

nachricht SF State astronomer searches for signs of life on Wolf 1061 exoplanet
20.01.2017 | San Francisco State University

nachricht Molecule flash mob
19.01.2017 | Technische Universität Wien

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>