Soap bubbles and jellyfish galaxies

Soap bubbles and jellyfish galaxies

Read time: 3 minutes

You probably know how to make soap bubbles. First, you put a ring of plastic or metal into a soap
bath, and gently pull it out again. The ring is now filled with a thin film of soap. If you hold the ring
still, nothing will happen. But if you start walking, holding the ring above your head, it leaves a
beautiful trail of soap bubbles behind.

The reason, of course, is the pressure of the air. It isn’t hard at all to move the ring itself through the
air. However, the feeble soap film is easily pushed back by the air that you’re moving through. That’s
why the soap is blown out of the ring.

In a remote cluster of galaxies, astronomers have studied a cosmic equivalent of a soap bubble toy.
The space between the galaxies in the cluster is filled with a very hot, tenuous gas – that’s the ‘air’.
One of the galaxies in the cluster is moving through this gas at a pretty high velocity – that’s the
‘ring’. As a result, the thin gas in the galaxy – the ‘soap film’ – is pushed out and left behind.
Astronomers call this process ‘ram-pressure stripping’.

The galaxy and its cosmic ‘soap bubbles’ have been imaged in detail by the Hubble Space Telescope.
Together, they look a little bit like a jellyfish, with thin ‘tails’ trailing behind. Using the European Very
Large Telescope in Chile, astronomers have also detected the glow of hot hydrogen gas in the tails.
Now, ALMA has also studied the jellyfish galaxy. ALMA detected the submillimeter radiation from
carbon monoxide molecules within the gas flows (shown as orange knots in the image). It is the first
time that cold, molecular gas has been detected in a ram-pressure stripped galaxy.

The new observations provide scientists with more information on the motion of the galaxy, and on
the interaction between the galaxy and the tenuous gas in the cluster. They may also shed light on
the unexplained bursts of star formation that occur in the ‘tails’.


The jellyfish galaxy studied by ALMA is officially known as ESO 137-001. The galaxy is part of the
Norma cluster. The Norma cluster is named after the southern constellation Norma, in which it is
located, at a distance of some 220 million light-years. The cluster contains many hundreds of
galaxies. ESO 137-001 is moving towards the center of the cluster at a velocity of seven million
kilometers per hour. As a result of this fast motion, gas is pushed out of the galaxy, forming a
250,000 light-year long tail.


The ALMA observations of carbon monoxide in the tail of the jellyfish galaxy ESO 137-001 were
carried out by Pavel Jáchym and his colleagues. Pavel is an astronomer at the Czech Academy of
Sciences in Prague. He teamed up with ten other astronomers, from the United States, Canada, the
United Kingdom, Australia, Portugal, and France. The new observations are published in The
Astrophysical Journal.