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A Ludwig Maximilian University (LMU) team has furnished a model for revealing what the color of a galaxy tells about its distance, to be used for measuring cosmic structures.<\/p>\n
Our universe is around 13.8 billion years old. Over the vastness of this time, the tiniest of initial asymmetries have grown into the large-scale structures we can see through our telescopes in the night sky: galaxies like our own Milky Way, clusters of galaxies, and even larger aggregations of matter or filaments of gas and dust.<\/p>\n
How quickly this growth takes place depends, at least in today’s universe, on a sort of wrestling match between natural forces: Can dark matter, which holds everything together through its gravity and attracts additional matter, hold its own against dark energy, which pushes the universe ever further apart?<\/p>\n
“If we can precisely measure the structures in the sky, then we can observe this struggle,” says LMU astrophysicist Daniel Gr\u00fcn.<\/p>\n
This is where telescopic observation projects come in, capturing large swaths of the sky very precisely in images. For example, there is the Dark Energy Survey with the Blanco telescope in Chile and the recently commissioned Euclid satellite. LMU scientists have been involved in both projects, including in leadership roles, for years.<\/p>\n
Although precisely determining the distances of individual structures and galaxies from us is not always easy, it is vitally important. After all, the further away a galaxy is, the longer its light has been traveling to us, so the snapshot of the universe revealed by its observation is therefore older. An important source of information is the observed color of a galaxy, which is measured by ground-based telescopes like Blanco or satellites like Euclid.<\/p>\n
A new study by a team led by Jamie McCullough and Daniel Gr\u00fcn, which has been published in the journal Monthly Notices of the Royal Astronomical Society<\/i>, has analyzed the largest dataset to date and sheds light on what the color of various galaxies actually says about their true distance.<\/p>\n
In principle, the distance of a galaxy can be precisely determined by means of spectroscopy. This involves measuring the spectral lines of distant galaxies. As the universe as a whole is expanding, these appear to have a longer wavelength, the further away from us a galaxy is located. This is because the lightwaves of distant galaxies are stretched out on the long journey to us.<\/p>\n
This effect, known as redshift, also changes the apparent colors that the instruments measure in the image of the galaxy. They appear redder than they are in reality. This is similar to the Doppler effect we hear in the apparent pitch of an ambulance’s siren as it passes us and moves away.<\/p>\n \n
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