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Hanny Van Arkel - 'The Accidental Astronomer'

It started with a strange blue smudge on a computer screen!


Hanny van Arkel was listening to a lot of Queen back in 2007. She wasn’t a big galaxy watcher at the time, but when Queen guitarist Brian May started promoting a citizen astronomy project called 'Galaxy Zoo', she decided to check it out. Then a few months later, she discovered a Quasar Ionisation Echo — and everything changed!

Galaxy Zoo began with a call for volunteers to help classify distant galaxies in space telescope images. The collaborative project made spectacular discoveries, leading a family of similar projects - collectively known as the "Zooniverse".


The original SDSS image seen by Hanny


That mysterious blob, spotted by a Dutch primary school teacher during a few idle hours one evening, has become one of the most remarkable recent discoveries in astronomy. Hanny's Voorwerp (meaning "Hanny’s object" in Dutch), named after its discover, is providing scientists with a striking new window on the universe. When the news broke, it turned Miss Van Arkel into a minor celebrity in the astronomy world.


"The first time someone asked me for my autograph ,I thought they were joking" , she said.


A decade later, another 20 of these rare intergalactic objects are thought to have been found - although many remain "candidate" voorwerpen until they can be examined more closely.

Scientists suggests that these distant clouds of glowing gas can provide an insight about what our neighbouring galaxies have been doing in the previous few thousand years. Although in galactic scale, Voorwerp is clearly not a galaxy because it does not contain any stars. Detailed spectrographic observations since its discovery suggest that it is a giant cloud of gas that is glowing an unusual green colour.


That raises an obvious question: what is causing the gas to glow?


Hayden Rampadarath at the Joint Institute for VLBI in Europe, based in the Netherlands and a multitude of friends, provide an answer. Their data comes from a new study of the nearby spiral galaxy IC 2497 using a couple of very long baseline interferometers to study the region at various wavelengths. Their conclusion is that, like many galaxies, IC 2497 contains a massive black hole at its centre. The in fall of matter into the black hole generates a cone of radiation emitted in a specific direction. The great cloud of gas that is Hanny’s Voorwerp just happens to be in the firing line. The black hole radiation is ionising the gas, causing it to glow green.

Another idea was put forward in recent years,which says that some 100,000 years ago, IC 2497 suddenly underwent a dramatic outburst of quasar-like radiation and then became quiet. What we see today from this cloud of gas,is simply a reflection of this outburst. In other words, Hanny’s Voorwerp is a quasar light echo.


What is " Quasar Light Echo "?

{Fig :Reflected light following path B arrives shortly after the direct flash following path A but before light following path C. B and C have the same apparent distance from the star as seen from Earth.}


First of all, a light echo is a physical phenomenon caused by light reflected off surfaces distant from the source, and arriving at the observer with a delay relative to this distance. The phenomenon is comparable to an echo of sound, but due to the much faster speed of light, it mostly only manifests itself over astronomical distances.


HsV (Hanny's Voorwerp) is, specifically, categorised as a quasar light echo, meaning that IC 2497 was once a quasar. Given that HsV appears to be 45,000 to 70,000 light years away from the spiral galaxy, IC 2497 must have shut off at least 45,000 to 70,000 years ago. However, the activity was likely transient, lasting for perhaps 100,000 years. During this period, a dwarf galaxy, partially torn apart by tidal forces from the quasar, became HsV, re-emitting the quasar’s light.



Citizen science project is booming. Today, anyone with a computer or a smartphone can participate in research in astronomy, oceanography, medicine, zoology and beyond. So if an English teacher (and citizen scientist) Hanny Van Arkel can discover a rare astronomical object in her spare time, maybe you can too!

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