"What is essential is invisible to the eye", as Antoine de Saint-Exupery wrote.
This is certainly true for starburst galaxies. Like human beings, galaxies and stars within them are born, they grow and eventually die. Starbursts represent the youthful phase in a galaxy's life. Our Milky Way may instead be considered as a 'middle age' galaxy. So, studying starbursts enable us to effectively peer back into our own Galaxy's past.
These galaxies are real 'baby boomers', creating new, young stars faster than many Milky Way-like galaxies put together. The dusty 'ash' left over by successive generations of stars blocks out much of the starlight, rendering them invisible to wavelengths which the eye is sensitive to. The bulk of the radiative energy of starbursts emerges instead at longer wavelengths. So one must turn to the infrared in order to understand the nature of these cosmic stellar factories.
Now, Japan's Subaru telescope has been used to produce a new view [1] of the most famous of starbursts, Messier 82. Messier 82 is the nearest of such systems, at about 11 million light years from us. Located just above the front end of the Big Dipper, it is easily visible under dark northern skies to amateur astronomers equipped with a decent pair of binoculars.
Previous observations with infrared telescopes have found a very strong wind emanating from the galaxy. This 'superwind' is composed of dusty gas and extends over many hundreds of thousands of light years [2]. Being ejected from the starburst at speeds of about half a million miles an hour, this storm sweeps up material from the central regions and deposits it far and wide over the galaxy and beyond. The elements within this material form the seeds for solar systems like our own, and perhaps life as well. The dusty superwind glows brightly in the infrared because it is heated by billions of bright newly formed stars.
However, all space observatories are restricted in size, which limits the extent to which fine details can be resolved.
The Subaru telescope, with a large mirror 8 meters in diameter, allows a sharp, magnified view of the core of the galaxy. The infrared camera attached to the telescope is called COMICS. Together, they give us the capability to capture fine details, equivalent to the ability to see a five yen coin from a distance of 10 kilometers [3]. The final result is an image showing the base of the dusty superwind and young star clusters in spectacular detail, better than can be expected from any current or future space mission being planned.
The wind is found to originate from multiple ejection sites spread over hundreds of light years, rather than emanating from any single cluster of new stars. We can now see individual 'pillars' of fast gas, and even a structure resembling the surface of a 'bubble' about 450 light years wide. COMICS is especially sensitive to the presence of warm dust, which is found to be more than 100 degrees hotter than the bulk of material filling the galaxy. Wide spread, continuous flow of energy from young stars into the galactic expanse is what keeps this dust hot.
Further insight comes from combining the infrared image with Hubble's near-infrared and Chandra's X-ray data, producing the beautiful mosaic shown in [4]. This provides the first opportunity to isolate the infrared properties and hence study the broad spectrum radiation of all kinds of objects spread over the plane of the galaxy, including supernovae, star clusters and black holes. Interestingly, the infrared radiation, which maps out warm gas and dust, appears in regions where the stars do not, meaning that many more stars are likely to be hidden behind the dust.
So, ultra-sharp pictures of starbursts with Subaru/COMICS enable important gains in our understanding of these complex astrophysical systems. One exciting question which remains to be answered, however, is whether or not Messier 82 hosts an actively growing supermassive black hole. Detailed analysis of the new infrared data combined with X-rays does not find any such object. But all large galaxies could well contain these monsters, which are known to grow and evolve in conjunction with stars. Messier 82 may be no exception, and the search for its big black hole must continue.
