Ernst Julius Öpik scholarship laureate Maarja Kruuse likes unanswered questions

Kairi Janson | 24.11.2017

„The most exciting part, of course, is getting answers to research questions and providing the science community with new information,“ says recent Ernst Julius Öpik scholarship laureate Maarja Kruuse. And by information, Kruuse means knowledge about the evolution of our whole Universe: her PhD thesis is about the structure of the Universe.

Maarja Kruuse 2017

„The evolution, structure and dynamics of the Universe depend among other things on the dark matter and the dark energy. If you studied the visible structure made up of galaxies, dark matter and dark energy could be better understood,“ explained Kruuse, second year PhD student of University of Tartu. The cosmic network holds information about the physics of the structure formations and influences the evolution of the objects it contains of.

Filaments as pearl necklaces

Kruuse “made it to space” on the first year of her master’s studies when she was studying mathematical statistics in University of Tartu and realized she wanted to connect her thesis with astronomy. She looked up the contacts of Tartu Observatory and sent an e-mail. Thereupon Elmo Tempel, her future supervisor, contacted Kruuse. Tempel has received the Ernst Julius Öpik scholarship himself twice.

By now, Kruuse is junior researcher at Tartu Observatory and writing her PhD thesis on the morphology of the cosmic web: connection between galaxy groups, filaments, sheets, and voids.

“The Universe has a cellural structure,“ Kruuse described. „It is made up of galaxies that are divided into different systems. Some of those are long string-like bridges and other structure elements are compact.“

Till now, Kruuse has been studying the first ones: the long curved bridges made of galaxies called filaments. Filaments are one of the most dominant features of the cosmic web. Kruuse and co-authors have described the pattern of galaxies in filaments as pearl necklaces – pearls have a certain distance between them in a necklace. Galaxies and galaxy groups have a tendency to have a preferred distances between them along the filamentary spine as well.

The question of photometric galaxies

In her thesis, Kruuse is researching the catalogue of filamentary spines derived from large-scale spectroscopic galaxy data. In the case of spectroscopic redshift galaxies, the distance of the galaxy is determined by using the redshift and measured straight from the light spectrum.

The distance evaluation is precise when it comes to spectroscopic redshift galaxies, but there is no such accuracy with photometric redshift galaxies. “If we look at the photometrical redshift galaxies, we don’t know their exact location in the 3-dimensional Euclidean space,” Kruuse stated. Their distance estimations have quite vast errors, which makes the use of these distances not sensible.

Kruuse and her supervisors (besides Tempel also Radu Stoica and Peeter Tenjes) have been interested in whether the same filaments can be seen with photometric galaxies as well. By now, they have been able to prove that photometric galaxies do show the signal of the same filamentary structure. The ongoing work is creating a basis for using these photometrical redshift galaxies in future filamentary pattern modeling from observational galaxy data.

Unanswered questions

Kruuse is using the filamentary spine catalogue, which is gained by using the Bisous model on observed spectroscopic galaxy data. In her thesis, Kruuse can connect her two majors: mathematical statistics and physics. „You can think of mathematical statistics as a tool to answer questions that arise in other scientific fields,“ Kruuse stated. „Cosmology is one of those fields that uses statistic methods widely.“

Being asked which half – the mathematics or cosmology one – is more exciting for herself, Kruuse states that the most exciting part are the questions that need to be answered.

A PhD student’s work day is not the classic one

One can also discuss about unanswered questions in summer schools, which Kruuse is also always happy to visit. During her first year of PhD studies, she went to three different summer schools that all took place in different countries.

When Kruuse is not inside the science world, she loves to sport. From spring to early autumn Kruuse loves to ride a road bike and from autumn to spring she practices Pilates and does strength exercises. “Sports helps to keep both the mind and body healthy and strong,“ Kruuse believes.

She thinks that sport is also important because being a PhD student means a lot of sitting and working behind the computer. But that is not the biggest challenge regarding her research. Given the enormous amount of data, even the easiest filtrations and calculations can be time-consuming. This is why Kruuse finds recognition very pleasant and motivating. “A PhD student’s work day does not always end when the night comes and sometimes doesn’t even stop for the weekend,” Kruuse said. She thinks that being appointed the scholarship helps a PhD student value their work themselves as well.