It would take Hubble 85 years to match what Nancy Grace Roman will see in 63 days

Less than a year and a half into its primary mission, it The James Webb Space Telescope (JWST) has already revolutionized astronomy as we know it. Using its advanced optics, infrared imaging and spectrometers, JWST has provided us with the most detailed and stunning images of the cosmos to date. But in the coming years, this telescope and its peers will be joined by another next-generation instrument: Nancy Grace Roman Space Telescope (RST). Aptly named after “Hubble’s Mother”, Novel will pick up where Hubble ended by looking back to the beginning of time.

As Hubble, RST will have a 2.4 meter (7.9 ft) primary mirror and advanced instruments to take images at different wavelengths. However, RST will also have a giant 300 megapixel camera – the Wide Field Instrument (WFI) – which will enable a field of view two hundred times larger than Hubble’s. In a recent study, an international team of NASA-led scientists described a simulation they created that previewed what the RST could see. The resulting data set will enable new experiments and opportunities for RST when it takes place in 2027.

The team included scientists from the Astrophysics Science Division at NASA’s Goddard Space Flight Center, the Flatiron Institute’s Center for Computational Astrophysics, the National Astronomical Observatory of Japan (NAOJ), the South African Astronomical Observatory (SAAO), the Space Telescope Science Institute (STScI), the European Southern Observatory (ESO), Mitchell Institute for Fundamental Physics and Astronomy, Ecole Polytechnique Fédeérale de Lausanne (EPFL) and several universities.

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From the side of the simulated universe, each dot represents a galaxy whose size and luminosity correspond to its mass. Credit: NASA/GSFC/A. Yung

The simulation was based on a well-tested theory of galaxy formation that includes the most widely accepted cosmological model – the Lambda Cold Dark Matter (LCDM) model. This allowed the team to simulate five cones of light measuring two square degrees in diameter (about ten times the apparent size of a full moon) that contained over 5 million galaxies each. These galaxies were distributed across the redshift spectrum (z=1-10), corresponding to distances of 1 million and over 13 billion light years.

The paper describing their results was published in Monthly Notices of the Royal Astronomical Society in December 2022. Aaron Yung, a postdoctoral fellow at NASA’s Goddard Space Flight Center who led the study, said in a recent NASA press release:

“The Hubble and James Webb space telescopes are optimized for studying astronomical objects in depth and at close range, so they are like looking at the universe through the eye of a pin. To solve cosmic mysteries on the largest scale, we need a space telescope that can provide a far greater visibility. That’s exactly what Roman is designed to do.”

When it begins operations, these and other simulations will provide a framework for astronomers to compare with observational data. This will allow scientists to scrutinize their astrophysical and cosmological models, with implications for everything from the formation and evolution of galaxies to dark matter, dark energy and much more. This will be possible thanks to His novel ability to combine a field of vision two orders of magnitude larger than Hubble (and an angular resolution to match) with advanced spectroscopy.

For example, by observing how dark matter causes light from more distant objects to be distorted and amplified (gravitational lensing), Novel will help us see how Dark Matter Haloes evolved over time. While it would take other space telescopes closer to a century (or more) to map these vast cosmic structures, Novel could do the same job within 63 days. In addition to the wide field of view, this will be made possible thanks to the observatory’s fast swing speed and rigid structure. Basically, Novel can move quickly from one target to the next since the components (such as the solar panels) are fixed in place.

This means that vibrations caused by repositioning will subside quickly, reducing the waiting time between image captures. “Roman will take about 100,000 images each year,” said Jeffrey Kruk, a research astrophysicist at NASA Goddard (and a co-author on the paper). “Granted Novelits larger field of view, it would take longer than our lifetime even for powerful telescopes like Hubble or Webb to cover as much sky.”

Another exciting aspect of RST is how it will collaborate with other observatories to study the universe in more detail. This includes identifying targets for follow-up studies using Hubble‘s wider wavelength coverage and Webbmore detailed infrared observations. This will provide in-depth studies of cosmic objects ranging from galaxies and galaxy clusters to exoplanets and objects in the solar system. Yung said:

“Roman will have the unique ability to match the depth of the Hubble Ultra Deep Field, yet cover several times more sky area than broad surveys such as the CANDELS survey. Such a full view of the early universe will help us understand how representative Hubble and Webb’s snapshots are of what it was like then.”

“Simulations such as these will be crucial in linking unprecedented large-scale galaxy surveys from Roman to the invisible scaffolding of dark matter that determines the distribution of these galaxies,” added Sangeeta Malhotra, an astrophysicist at Goddard and co-author of the paper. All told, the simulation provides forecasts for the number density of galaxies, star formation rates (SFR), field-to-field variance, and angular two-point correlation functions. It also shows how future wide-field surveys will be able to improve these measurements compared to current surveys.

In addition to RST, the team’s simulations also provide photometry for several other instruments at upcoming observatories. This includes ESA Euclid mission and the Vera Rubin Observatory, a space-based telescope that will study Dark Energy and a ground-based observatory that will characterize millions of objects in the Solar System (respectively). Both missions are expected to launch or begin gathering light sometime later this year. The coming years will be an exciting time for astronomers and cosmologists. And with any luck, revealing!

Further reading: NASA, MNRAS

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