Astronomers believe that these high density molecular clouds located in IC4954/4955 often participate in star formation when supernova explosions and intense radiation from young high-mass stars sweeps the interstellar material together into these high-density regions. AKARI infrared observations over the wavelength range from 9 to 160 micrometres detected the evidence of such star formation (marked by green crosses).

The image is a three-colour composite image from AKARI’s 9 (blue), 11 (green), and 18 (red) micrometre data. The two arc-like structures visible in the panel are formed by a young-massive star (not seen in the image) at the centre of the nebula, sweeping material outward by their strong radiation pressure.

Credits: JAXA

The white dots in the image are infrared stars. The apparent distinct hollow in the middle of the image is about a hundred light years in diameter. It is suspected that an even earlier, first generation star (the ‘grandparent’) formed around several to ten million years ago, inducing the star formation of the second generation including the IC4954/4955 region. This is how AKARI data encompasses the cycle of star formation over three complete generations, over spatial scales of one to a hundred light years, in infrared light.

Credits: JAXA

Astronomers believe that these high density molecular clouds located in IC4954/4955 often participate in star formation when supernova explosions and intense radiation from young high-mass stars sweeps the interstellar material together into these high-density regions. AKARI infrared observations over the wavelength range from 9 to 160 micrometres detected the evidence of such star formation (marked by green crosses).

The left panel is a three-colour composite image from AKARI’s 9 (blue), 11 (green), and 18 (red) micrometre data. The two arc-like structures visible in the panel are formed by a young-massive star (not seen in the image) at the centre of the nebula, sweeping material outward by their strong radiation pressure.

The right panel is a colour-composite image from far-infrared data, showing that the arcs are also heated by the central star and appear in blue. This image also shows lower-temperature material in the nebula (seen as red); that this would normally be invisible in the optical wavelengths since interstellar material masks the light from coming from behind. These cooler regions contain large amounts of interstellar material that will eventually form a new generation of stars.

Credits: JAXA

In the final stage in the life of stars much heavier than our own Sun, a supernova explosion ejects matter into interstellar space, creating a supernova remnant. The matter ejected consists of newly synthesized elements created inside the star’s core. The catastrophic explosion disturbs interstellar material creating shock waves over great distances, thus making supernovae essential contributors in the internal evolution of galaxies.

B0104-72.3 is a well-known supernova remnant that has been observed with radio and X-rays, (although not particularly bright at these wavelengths). Infrared observations help trace the interaction between the supernova remnant and the interstellar medium, but this understanding has until recently been limited due to the lack of data.

B0104-72.3 was observed by AKARI at four different infrared wavelengths, the intensity ratios of which reveal the presence of a shock at the interaction between the expanding remnant and the surrounding molecular clouds. This implies that the precursor was a high-mass star. In this manner, observations with AKARI are expected to play a key role in understanding the evolution of interstellar material through studies of interaction processes with the supernova remnant.

Credits: JAXA

Globular clusters are dense spherical groups of about one million stars. NGC104 is thought to have formed about 11 thousand million years ago (approximately the age of the Milky Way). The massive stars in the cluster have long burnt out, and those that currently light the cluster are of mass similar to that of our Sun - or rather to what our Sun will evolve into approximately 6 thousand million years from now.

The stars of NGC 104 with similar mass to our Sun have already extinguished the hydrogen in their cores – the fuel required for nuclear fusion – and proceeded to later stages of stellar evolution to become red-giant stars. Sun-like stars undergo ‘mass-loss’ at this stage: they eject about 40 per cent of their mass into interstellar space becoming ‘white dwarf’ stars. The mass loss in the early red-giant phase, important for understanding the evolution of galaxies, had been predicted only in theory so far.

The bright red stars seen in the image are mostly in the final stages of the red-giant phase with mass loss rates as high as one millionth of their mass per year. Stars in the earlier red-giant phase are seen as slightly darker. The star marked in the bottom-left corner has a high rate of mass loss while still a young red-giant, confirming the presence of mass-loosing younger red-giants for the first time. The presence of other similar young red giants in the cluster without mass-loss implies that the phenomenon in young red-giants is not continuous but rather episodic in nature, occurring sporadically over relative short periods when put into a cosmological context. Further analysis and modelling will enable to the scientists to understand the future evolution of our Sun, and the effect on the Solar System.

Credits: JAXA

UGC05101 is situated in the constellation Ursa Major, approximately 550 million light years away from the Earth. Termed an ‘ultraluminous infrared galaxy,’ the total energy it emits in the infrared alone is about one trillion times more than that of the Sun. However, the central region is covered by a thick interstellar medium and can only be observed in the infrared. Observations with AKARI have revealed evidence for active phenomena in the central part of this galaxy.

The feature seen around 4.5–5 micrometres is caused by absorption by carbon monoxide (CO) molecules in the gas phase. It is very broad, indicating that the temperature of this molecular gas is over 500 degrees Centigrade. It has been postulated that at the centre of UGC05101 is a giant black hole, of mass more than a million times that of our Sun. In this case, the material around it would be expected to radiate enormous amounts of energy as it slowly tumbles into the black hole. It is suspected that the detected molecular gas is heated by radiation from near the black hole.

Credits: JAXA

It has been postulated that at the centre of UGC05101 is a giant black hole, of mass more than a million times that of our Sun. In this case, the material around it would be expected to radiate enormous amounts of energy as it slowly tumbles into the black hole.

Credits: JAXA

Galaxies in which active star formation is taking place emit most of their energy as infrared radiation from the interstellar material heated by the light from the young hot stars. The light observed from the distant galaxies, has long left the galaxies and is stretched (or ‘red-shifted’) due to the expansion of the Universe. This is why it is observed at wavelengths longer than the original emitting wavelengths. Due to the redshift, observations with ESA’s Infrared Space Observatory (ISO) revealed that the number of faint, distant galaxies increased drastically when observed at 15 micrometres. The original emitting wavelength was 7 micrometres, approximately 6 thousand million years ago, and has been redshifted to 15 micrometres during its journey across the universe.

This emission feature around 7 micrometres, due to the characteristic emission from organic materials in the interstellar medium, is stronger in regions of active star formation. Thus, the ISO observations of a very small area of the sky containing only 24 galaxies already showed that active star formation took place at this epoch in the history of the Universe.

The area observed by AKARI is about three times wider than that of ISO. AKARI detected around 280 galaxies in this region, confirming the increase in the number of galaxies at 15 micrometres implied by the earlier ISO observations. Comparable numbers of even fainter galaxies have been discovered with AKARI, leading to the conclusion that the star formation activity was already intense even earlier than 6 thousand million years in the past. Similar deep surveys over the entire wavelength range (from 2 to 24 micrometres) are being carried out with AKARI. These data will provide a definitive description of the evolution of galaxies over the lifetime of the Universe.

Credits: JAXA