ESA /NASA Hubble: The third way of galaxies - lenticular

Credit: ESA/Hubble & NASA

The subject of this image is NGC 6861, a galaxy discovered in 1826 by the famed Scottish astronomer James Dunlop.

Almost two centuries later we now know that NGC 6861 is the second brightest member of a group of at least a dozen galaxies called the Telescopium Group, otherwise known as the NGC 6868 Group, in the small constellation of Telescopium (The Telescope).

The famed Scottish astronomer James Dunlop Credit: Wiki

This NASA/ESA Hubble Space Telescope view shows some important details of NGC 6861. One of the most prominent features is the disc of dark bands circling the centre of the galaxy.

These dust lanes are a result of large clouds of dust particles obscuring the light emitted by the stars behind them.

Dust lanes are very useful for working out whether we are seeing the galaxy disc edge-on, face-on or, as is the case for NGC 6861, somewhat in the middle. Dust lanes like these are typical of a spiral galaxy.

The dust lanes are embedded in a white oval shape, which is made up of huge numbers of stars orbiting the centre of the galaxy. This oval is, rather puzzlingly, typical of an elliptical galaxy.

So which is it, spiral or elliptical? The answer is neither! NGC 6861 does not belong to either the spiral or the elliptical family of galaxies.

It is a lenticular galaxy, a family which has features of both spirals and ellipticals.

The relationships between these three kinds of galaxies are not yet well understood. A lenticular galaxy could be a faded spiral that has run out of gas and lost its arms, or the result of two galaxies merging.

Being part of a group increases the chances for galactic mergers, so this could be the case for NGC 6861.

ESA NASA Hubble Image: Mysterious Old Spiral

Credit: ESA/Hubble & NASA, Acknowledgement: Judy Schmidt

This striking cosmic whirl is the center of galaxy NGC 524, as seen with the NASA/ESA Hubble Space Telescope.

This galaxy is located in the constellation of Pisces, some 90 million light-years from Earth.

NGC 524 is a lenticular galaxy.

Lenticular galaxies are believed to be an intermediate state in galactic evolution — they are neither elliptical nor spiral.

Spirals are middle-aged galaxies with vast, pin wheeling arms that contain millions of stars.

Along with these stars are large clouds of gas and dust that, when dense enough, are the nurseries where new stars are born. When all the gas is either depleted or lost into space, the arms gradually fade away and the spiral shape begins to weaken.

At the end of this process, what remains is a lenticular galaxy — a bright disc full of old, red stars surrounded by what little gas and dust the galaxy has managed to cling on to.

This image shows the shape of NGC 524 in detail, formed by the remaining gas surrounding the galaxy’s central bulge. Observations of this galaxy have revealed that it maintains some spiral-like motion, explaining its intricate structure.

NASA /ESA's Hubble Image: A stranger in the crowd

Credit: European Space Agency

The constellation of Virgo (The Virgin) is the largest of the Zodiac constellations, and the second largest overall after Hydra (The Water Snake).

Its most appealing feature, however, is the sheer number of galaxies that lie within it.

In this picture, among a crowd of face- and edge-on spiral, elliptical, and irregular galaxies, lies NGC 4866, a lenticular galaxy situated about 80 million light-years from Earth.

Lenticular galaxies are somewhere between spirals and ellipticals in terms of shape and properties.

From the picture, we can appreciate the bright central bulge of NGC 4866, which contains primarily old stars, but no spiral arms are visible.

The galaxy is seen from Earth as almost edge-on, meaning that the disc structure—a feature not present in elliptical galaxies—is clearly visible.

Faint dust lanes trace across NGC 4866 in this image, obscuring part of the galaxy's light.

To the right of the galaxy is a very bright star that appears to lie within NGC 4866's halo.

However, this star actually lies much closer to us; in front of the galaxy, along our line of sight.

These kinds of perspective tricks are common when observing, and can initially deceive astronomers as to the true nature and position of objects such as galaxies, stars, and clusters.

This sharp image of NGC 4866 was captured by the Advanced Camera for Surveys, an instrument on the NASA /ESA Hubble Space Telescope.