Science

Ruling the Milky Way

‘It’s like nature does what you want’

Amina Helmi’s thesis on the origin of our Milky Way was a major breakthrough in astronomy. She has been a rising star ever since. This Friday she was awarded the most
important science award in the Netherlands: the Spinoza Award.
Text by Tim Bakker / Photo’s by Reyer Boxem ©RU  / Translation by Sjef Weller

Gaia’s treasure trove

Amina Helmi’s list of breakthroughs has only grown since she was inducted in the Royal Netherlands Academy of Arts and Sciences. The readings from the European Gaia
satellite, available since April 2018, were of key importance.

‘For astronomers, there are two eras: before Gaia and after Gaia’, Amina Helmi said on the day the Gaia measurements on 1.7 billion stars were released. It was a treasure’trove for astronomers’.
The explosion of sientific data for astronomers was unprecedented. Gaia presented the sky positions and brightnesses of nearly 1.7 billion stars, as well as distances, motions, and colour information for 1.3 billion.

Helmi was the leader of the group responsible for validating the data by asking ‘real’ scientific quiestions. She found that some satellite galaxies appear to be travelling
through space in pairs, like ‘space buddies’, while half of the satellites are moving relatively coherently – in a kind of flow – through space.

In the months that followed, Helmi published more papers with the Gaia data. In September she published an article in Nature, in which she described that our Milky
Way got a ‘kick’ when dwarf star system Sagittarius passed about 500 million years ago. It caused stars that used to rotate in a disc form to follow more intricate patterns that resemble a snail house.

In October another Nature publication followed. This time Helmi and her colleagues
found that the Milky Way gets much of its shape from a merger with another galaxy that
happened around ten billon years ago.

‘It’s like you are driving around on Mars’, says Amina Helmi, remembering the trip. Her destiny was at 2,635 meters height in the Atacama Desert in Chile, far from inhabited areas: the Very Large Telescope, VLT in short. This observatory, one of the most advanced in the world, provides her with data for her research into the history of our Milky Way. The contrast with her journey through the desert could hardly have been any starker, when we are waiting for the elevator, roughly 11,361 kilometres away, near the buzzing canteen of the Bernouilliborg.

We are on our way to the sixth floor, to the Blaauw Sterrenwacht. Today, this observatory, which was built in 2008, will function as a background for the photo to go with this story. In the elevator, Helmi makes a confession. ‘I’ve never been here before.’ That sounds strange for an astronomer working from Groningen, but for her research she needs heavier equipment than the Bernouilliborg’s Gratama Telescope.

Although this Groningen telescope has a primary mirror with a diameter of 40 centimetres and is one of the largest in the Netherlands, it comes nowhere close to the four VLT telescopes, each with a diameter of more then 8 meters. What’s more, light pollution, cloudy weather and vibrations – an astronomer’s biggest enemies – form a constant threat in Groningen.

Not to say that this would be of great importance to Helmi, she rarely uses a telescope. ‘But I work together with people who do use it. Most of the time, I work with computer models, based on data contributed by others.’ So this is not going to be the stereotypical tale of an astronomer who loved to gaze at the stars, she warns.

Sun and moon

Helmi grew up in Argentina, as a child of an Egyptian father and a Dutch mother. The first time she heard about astronomy was about 35 years ago, in her last year of primary school in Bahía Blanca. Her teacher explained how planets revolve around the sun and how we always get to see the same side of the moon. ‘I found that interesting and fascinating, but I was not thinking about it all day.’

‘As a child, I never had a telescope. And on Saturday afternoons, when the TV series Cosmos, with Carl Sagan, was broadcast, I’d rather go playing with my friends. The images were beautiful, but that was not enough to arouse my curiosity. But what I did find special, was that you could understand things, objects, that were so far away and impossible to touch. That you could figure out how they work. I liked being able to understand why things were the way they were.’

In high school, she was a crack at physics and maths, and until the very last moment she considered studying mathematics. Yet in the end, she decided to study astronomy at the university of La Plata. Out of the two universities she could choose from, that one was closest to home. ‘That choice did have something to do with the magical vastness of the universe. There is so much to be found, there are so many secrets that no one has discovered so far. And yet, everything behaves according to the same laws in nature as here on earth.’ Just finishing her study was not enough for her: she wanted to learn more about the Milky Way and about the world.

PhD research

By doing her PhD research at Leiden University, Helmi had a chance to fulfil both wishes at the same time. ‘That was not easy at first, since it was pretty unusual then that non-European students would be hired to carry out a PhD here.’ She nonetheless obtained a PhD studentship, and an Amelia Earhart grant worth 10,000 dollars allowed her to come to the Netherlands. After her arrival, she still had to break the language barrier. ‘Because my mom is Dutch, I already understood the language, but speaking Dutch was still difficult for me.’

For her thesis, Helmi investigated the prevalent hypothesis that large galaxies, like ours, are in part shaped by smaller and older systems colliding and fusing. But nobody had ever proved it for the Milky Way. She argued that if this would be the case you should be able to find traces of that process, in the shape of groups of stars from these old systems still moving together through the Milky Way.

Helmi searched for these group of star fossils… and found them! She proved something that – until that day – scientists could only assume. Her findings were noticed all over the world and this led to several awards. Not only is the proof that the Milky Way was in fact shaped by mergers with smaller galaxies a new step in the history of the Milky Way, it has also implications for how other galaxies in the universe have evolved.

Balance

It has already been 20 years since Helmi came to the Netherlands, and during that time a lot has happened. By now, she speaks Dutch fluently and lives happily together with her son Manuel (11) and her dog Sandy. Although Manuel shares his mother’s technical insight, he ‘fortunately’ has no plans to be an astronomer himself. ‘That would be too much astronomy in one household. I am already rather budy with my work, Manuel brings balance to my life.’

For one of her projects, Helmi was involved in the design of Gaia, the newest satellite of the European Space Agency (ESA) that was launched in 2013. This satellite measures the location and motion of a billion stars in our Milky Way. By comparison: the ESA satellite Hipparcos, Gaia’s predecessor that provided Helmi with data for her promotion research in 1997, ‘only’ delivered information about a 100,000 stars and was far less accurate. No wonder that Helmi – together with the rest of the astronomy community – could not wait to see the first results in September 2016.

It is a small world, says Helmi. ‘It is fairly easy to get to know virtually everyone. People treat each other well and are very passionate, too, that is what makes it so much fun!’ But at the same time, there is a lot of competition amongst astronomers as well. From the moment the Gaia data were made public, it was everyone for themselves. And with so many data available, that is no sinecure.

A box of chocolates

‘I like to compare the Gaia data to a box of chocolates. There is so much to choose from! But if you want to answer all the questions at the same time, i.e. when you try to eat each and every chocolate in the box, you get sick. It just cannot be done. So first, you need to focus on one specific question and take it from there. The data are not in the form of a nice visual simulation of the universe, but a database with a billion rows and hundreds of columns.’

Still, she and her team were working almost day and night for one and a half month on end to process the results. The new data confirms Helmi’s findings and brings even more speeding stars from other systems to light, as can be seen in the video. But there is no time to relax. There is still so much data to be understood, and in April 2018, Gaia will provide a new batch of data.

She did not own a telescope as a child, and even now she rarely uses one. But as a professor at the Kapteyn Astronomical Institute of the Faculty of Science and Engineering, Helmi keeps investigating the history of our Milky Way. Last month, her accomplishments led to membership of the Koninklijke Nederlandse Akademie van Wetenschappen (Royal Dutch Science Academy, KNAW), a prestigious society of excellent scientists.

She has a long list of awards, research grants and prizes. In 2013, a planetoid was even named after her. Yet there is a point in her relatively short yet impressive career that she will never forget, and that was during her thesis. ‘The moment that my predictions turned out to be correct…’, she sighs. ‘I got a huge kick out of that! It is like nature is doing what you tell it to do. It is like you really get it.’

This is an updated version of an interview UKrant did with Amina Helmi in June 2017.

 

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