SPACE/COSMOS

Local Dwarf Galaxies May Preserve A Record Of The Infant Universe

 (A) Dark matter distribution in our neighborhood in the Universe, the so-called Local Group of galaxies. The two large dark matter halos correspond to those of the Milky Way and Andromeda galaxy; (B) zoom-in on the dark matter in and around a small halo ~700 million years after the Big Bang; (C-1 and C-2) stars and gaseous material in the simulated ultra faint dwarf galaxy, hosted in the centre of the small dark matter halo in panel B, in two different models for the conditions of the early Universe. We can see how the ultra-faint dwarf galaxy changes its properties depending on the model. The scale on each image is in units of light years.  (Image credit: J Sureda/A Fattahi/S Brown/S Avraham)

 

April 25, 2026

By Eurasia Review

Ultra-faint dwarf galaxies, tiny satellite galaxies orbiting the Milky Way, have long been seen as cosmic fossils. Now, a new study by researchers at the Oskar Klein Centre and the LYRA collaboration uses an unprecedented set of simulations to show just how powerfully these faint systems can reflect the conditions of the early Universe and tell us why some galaxies grew and others did not. 

Azadeh Fattahi is Associate Professor at the Oskar Klein Centre (OKC) and heading the research group which led this work, now published in Monthly Notices of the Royal Astronomical Society (MNRAS), together with collaborators from Durham University and University of Hawaii. She explains the scale of the project: 

“In this work we presented a brand-new suite of cosmological simulations focused on the faintest galaxies in the Universe, with an unprecedented resolution. These are by far the largest sample of such galaxies ever simulated at these resolutions.” 

Dwarf galaxies are often described as small cousins of the Milky Way. They form in small dark matter halos which are predicted by the standard model of cosmology. The faintest examples of such systems are extreme in both size and fragility, and lie on the boundary of our knowledge about galaxy formation and dark matter. 

“The smallest galaxies are called ultra-faint dwarf galaxies, which are a million times less massive than the Milky Way or even smaller,” Fattahi says. “Due to their small size these galaxies have proven very difficult to model and simulate.”  

This new simulation suite represents a major step forward, enabling a systematic view of how these galaxies form and evolve. 

A down-to-earth analogy  

“A useful analogy is to plants and crops and how the way they grow is sensitive to the weather conditions”, says Shaun Brown who led the study while working at OKC and Durham University. “In the same way that the yield of a crop in summer can indirectly tell you a lot about what the weather in spring must have been like, the properties of faint dwarf galaxies today can tell us a lot about the conditions, or weather, of the Universe at a much earlier time.” 

What makes the results especially timely is that the simulations do more than reproduce faint dwarf galaxies – they suggest that these local objects can act as a probe of the Universe’s earliest “climate”. The team explored how different assumptions about the early radiation environment influence which small dark matter haloes manage to form stars at all. 

“In the paper we studied two different assumptions about the properties of the early Universe when it was less than 500 million years old, to understand the effect on the properties of these small galaxies today when the Universe is 13 billion years old,” Brown explains. 

The outcome was striking: 

“We found that these small ultra-faint galaxies are very sensitive to these changes, while more massive galaxies, like our Milky Way, don’t really care,” he adds, “For the smallest galaxies, early conditions can decide whether they become visible galaxies – or remain starless dark matter halos.” 

Future research 

That sensitivity opens a clear path to testing early-Universe physics with upcoming observations.  

“Excitingly, in the near future we will have data from the Vera C. Rubin Observatory which will be able to find many more of these ultra-faint dwarfs around the Milky Way,” says Fattahi. 

Many astronomers hope the Vera C. Rubin Observatory can deliver a near-complete census of Milky Way satellite galaxies – and these simulations suggest that census may carry information far beyond our local neighbourhood.  

“Our work suggests that these upcoming observations of the very local Universe will be able to constrain what the Universe at its infancy looked like, something we currently cannot directly access with other observations.” 

The result is particularly relevant in light of recent discoveries of galaxies in the early Universe, by the James Webb Space Telescope (JWST), which is finding many surprises, in particular unexpectedly massive and bright galaxies in the early universe,” Fattahi notes. 

If the early Universe is producing surprises at large distances, then local relics from the same epoch, ultra-faint dwarfs, may provide an additional route to understanding what happened.

Reaching this regime came with major practical challenges. “Running these simulations is challenging, and extremely expensive in both time and computational resources,” Fattahi says.

In total it took more than six months to run all of the simulations. The scale of the data was also substantial: “The simulation also produces very large amounts of data (in total approximately 300 TB). This meant many of the old algorithms designed for smaller amounts of data needed updating and improving to effectively handle this new large amount of data.”

Work carried out on the COSMA 8 supercomputer

Most of the work was carried out on the COSMA 8 supercomputer, which is designed for simulation-driven research. Durham University’s Institute for Computational Cosmology hosts COSMA 8 on behalf of the UK’s DiRAC High Performance Computing Facility.

Looking ahead, Fattahi’s team plans to use the new suite to tackle questions that are still open in modern galaxy and structure formation, such as where we can find the very first generation of stars formed in the Universe or what do the properties of ultra-faint dwarf galaxies tell us about the nature of dark matter? 

NASA unveils new space telescope to give ‘atlas of the universe’


ByAFP
April 22, 2026


The Roman telescope will blast into space aboard a SpaceX rocket in a launch planned for September at the earliest - Copyright AFP SAUL LOEB

Charlotte CAUSIT

NASA unveiled a new telescope on Tuesday to scan vast swathes of the universe for planets outside our solar system and probe the mysteries of dark matter and dark energy.

The Roman space telescope is expected to discover tens of thousands of planets, possibly offering clarity abut how many could be out there.

“Roman will give the Earth a new atlas of the universe,” NASA administrator Jared Isaacman told a news conference at the Goddard Space Flight Center in Maryland, where the telescope went on display.

The 12-metre (39-feet), silvery contraption with massive solar panels will be transported to Florida ahead of a launch into space aboard a SpaceX rocket planned for September at the earliest.

Roman, which took more than $4 billion and over a decade to build, is named after astronomer Nancy Grace Roman, nicknamed the “Mother of Hubble” for her role in developing the landmark space telescope.

Thirty-six years after Hubble launched into space, revolutionizing astronomical observations, NASA hopes Roman will help to shed light on questions that remain unresolved.

Boasting a field of view at least 100 times larger than Hubble’s, the telescope will sweep across vast regions of space from its position 1.5 million kilometres (930,000 miles) from Earth.

The telescope will send 11 terabytes of data a day down to Earth, said Mark Melton, a systems engineer at Goddard Space Flight Center.

“In the first year, we’ll have sent down more data than Hubble will have for its entire life,” he told AFP.

The telescope’s wide-angle lens will allow NASA to conduct a census of the objects that make up our universe, said Nicky Fox, associate administrator for NASA’s Science Mission Directorate.

“Roman will discover tens of thousands of new planets outside our solar system. It will reveal billions of galaxies, thousands of supernovae and tens of billions of stars,” she said.

This wealth of information will enable NASA to tease out areas of interest that can then be investigated by complementary telescopes, such as the James Webb Space Telescope.



– Study the invisible –



But Roman will also study the invisible — dark matter and dark energy, whose origins remain unknown but which are thought to constitute 95 percent of our universe.

Dark matter is believed to be the glue that holds galaxies together, while dark energy pulls them apart by making the universe expand faster and faster over time.

Thanks to its infrared vision, the telescope will be able to observe light emitted by celestial bodies billions of years ago, effectively looking back in time to hopefully discover more about the two phenomena.

Complementing the work of Europe’s Euclid space telescope and the Vera Rubin Observatory in Chile, Roman will probe “how the dark matter structures itself throughout cosmic time” and “calculate how fast galaxies are moving away from us,” Darryl Seligman, an assistant professor of physics and astronomy at Michigan State University, told AFP.

These discoveries could fundamentally change our understanding of the structure of our universe, said astrophysicist Julie McEnery, who led the Roman project.

“If Roman wins a Nobel Prize at some point, it’s probably for something we haven’t even thought about or questioned yet,” said Melton.

Does Medicaid Expansion Help Or Hurt Hospital Finances? – Analysis

 April 24, 2026

By Damon L. Daniels

In debates over health care policy, one of the arguments against expanding access to health insurance is that this leads to increased utilization of emergency rooms – a phenomenon that would create serious problems for hospitals. But a review of the available research suggests that provisions in the Affordable Care Act that broadened access to insurance are not creating these problems – and in fact, states that did not take advantage of Medicaid expansion are more likely to see increases in uncompensated care costs for hospitals. 

Introduction

Prior to the expansion of health insurance coverage in the Affordable Care Act (ACA), people with insurance (whether commercial insurance or Medicaid coverage) were the groups with similar and highest shares of Emergency Department (ED) visits. People without insurance made much less use of EDs. They were discouraged from seeking health care in an ED in all but the most dire circumstances by their concerns about the cost of such care. Knowing that they could not afford to pay for care, they reasonably expected the unpaid medical debt to affect their credit reports and to interfere with their ability to rent an apartment or get a job. They also expected the unpaid debt to be sold to a collection agency and to be hounded and harassed as the agency pursued them for payment. 

This limited their use of ED visits for true emergency health conditions — like spiking blood pressure that could lead to a stroke if untreated, or a deep gash from a cooking accident that required immediate medical attention. In contrast, people with commercial insurance or Medicaid coverage knew that insurance would pay the ED bill and they would be responsible only for the copay, which would be waived if the patient was admitted to the hospital. 

Research examining ED use in the period following the ACA’s voluntary Medicaid expansion to the near-poor, who previously lacked health insurance, finds an increase in ED visits by the newly insured. This, however, need not be a negative for hospitals if hospital net revenue increased as a result of this population being covered by insurance and if the costs of uncompensated care went down due to the decrease in patients without insurance who would be unable to pay for care.

In this issue brief, we examine what happened to ED usage following Medicaid expansion as well as the effect on hospital finances.

Emergency Department (ED) Utilization

National Studies

National studies generally focused on ED utilization trends for people under age 65 that occurred before and after several provisions of the ACA went into effect, particularly state‑level expansions of Medicaid eligibility.1 Prior to these expansions, the highest shares of usage occurred among patients with private insurance or Medicaid access.2

Following Medicaid expansion, the highest shares of ED visits occurred among patients with Medicaid access, while the proportions of visits by uninsured patients declined. The sharpest changes in the insurance status of ED visitors happened during the first two to three years after a state expanded Medicaid coverage.3 Among the different types of insurance sources evaluated (private insurance, Medicaid, no insurance, and Medicare), the percentages of ED visits by patients with Medicaid as their primary insurance source were higher than those with private insurance, no insurance or Medicare access. ED visits among the uninsured declined following Medicaid expansion.

State Studies

Studies of ED utilization trends among states featured similar investigations of ED visits before and after major ACA provisions took effect. States that expanded Medicaid were typically compared to states that did not. Medicaid expansion was found to increase Medicaid’s overall share of ED visits and reduce the share of uninsured ED visits in several Medicaid expansion states.4 Moreover, the largest increases in shares of Medicaid ED visits occurred among states with the highest increases in Medicaid enrollment, especially among enrollees who were previously uninsured.5 Conversely, private insurance shares of ED visits typically decreased in Medicaid expansion states.

Low‑Acuity, Non‑Urgent, and Preventable ED Utilization

Findings are mixed regarding the role that Medicaid expansion plays in reducing the volume of ED visits for care that can otherwise happen through a regular doctor visit. Studies have found, for example, that in some cases recipients may receive care from a doctor prior to requiring care in an emergency department.6 Some researchers speculate that less medically urgent  conditions are potential factors for increases in ED visits due to the Medicaid expansions, but do not claim that it is a causal factor.7

Uncompensated ED Costs

National Studies

Several early national studies utilized data from the Centers for Medicare and Medicaid Services (CMS) and Internal Revenue Service (IRS) to estimate hospitals’ uncompensated care costs as a share of total hospital costs in ACA Medicaid expansion versus non‑expansion states, before and after expansion was available. This research finds that states that expanded Medicaid coverage saw reductions in their uncompensated care burdens. 

From CMS data, one study found that among expansion states, uncompensated care costs were reduced from 4.1 to 3.1 percent of total operating costs of hospitals between 2011–2014.8 Extending this study to include 2015, the same authors found that between 2013 and 2015, uncompensated care costs were lowered from 3.9 percent to 2.3 percent of operating costs, resulting in estimated savings of approximately $6.2 billion.9 Between 2011–2015, another study found that these costs were reduced by 1.5 percentage points (a 28 percent reduction overall).10 A third study using CMS data from 2011–2017 estimated a decline of 2.6 percentage points in average uncompensated care costs as a percentage of total expenses from 2013–2017, relative to the study’s 2011–13 pre‑Medicaid expansion period.11 This study also found that average annual Medicaid revenue as a percentage of total revenue rose by 2.5 percentage points between 2013–2017 among hospitals in Medicaid expansion states, while Medicaid revenue remained relatively unchanged among hospitals in non‑expansion states.

Similarly, a study using IRS data from 2010–2014 found that “net effect” hospital costs (the combined costs for uncompensated care and Medicaid payment shortfalls) fell by 1.6 percentage points among expansion states compared to non-expansion states, amounting to uncompensated care costs savings of 21 percent.12 Another IRS study found that through September 2020, uncompensated care costs in Medicaid expansion states were around 2.7 percent of all operating expenses, versus 7.3 percent for non‑expansion states.13

Studies also investigated the locations and types of hospitals most impacted by changes in uncompensated care costs. Uncompensated care costs were highest in states that did not implement the Medicaid expansion. Considering hospital geographies, research suggests that post‑Medicaid expansion coverage uptake may be higher in rural as opposed to urban hospitals,14 but uncompensated care costs were highest among rural hospitals in non‑expansion states. A 2014–2019 study found that uncompensated care as a percentage of a hospital’s total operating expenses was highest among hospitals in rural, non‑expansion states.15 Among only rural hospitals, this study also found that primarily non‑expansion states held the highest 2014 median uncompensated care shares; in fact, these proportions were higher in 2019. Regarding hospital types, studies found that savings can occur for both for‑profit and non‑profit hospitals.16

Disproportionate‑share hospitals (DSHs), which treat an outsized number of low-income patients, have also experienced notable reductions in uncompensated care. A study that measured these reductions in terms of the number of days that a hospital bed is occupied (referred to as “quantity of care”) found that uncompensated days per bed decreased 35 percent in 2014, relative to the years 2011–2013; DSHs in expansion states also experienced 1.4 fewer uncompensated care days per bed than non‐DSH hospitals in 2014, relative to hospitals in non‑expansion states.17          

Looking forward, the presumption is that any rollbacks to the policies that expanded health care coverage will reverse the gains in access and savings evidenced by the findings above. These gains were only enhanced during the COVID-19 period. Through the “American Rescue Plan Act,” Congress passed temporary provisions that (1) raised incentives for states that had not already expanded Medicaid access to low‑income adults to do so, and (2) expanded the ACA’s premium tax credits.18 As the state incentives expired in March 2023,19 and the premium tax credits expired at the end of 2025,20 researchers at the Urban Institute have projected that these reversions – and especially, the omission of any extension of the premium tax credits through the “One Big Beautiful Bill Act” – would yield drastic 2026 consequences for uncompensated care costs. The Urban Institute expects increased demand for uncompensated health care of 12 percent, or $7.7 billion, compared to demand with the premium tax credits still in place. Hospitals are projected to incur approximately $2.2 billion of these increased costs.21

Conclusion

Studies of ED visits and their effects on the financial viability of hospitals lead to two conclusions. First, people with insurance account for a larger share of ED visits. And second, providing insurance coverage to people who formerly did not have health insurance leads to substantial improvements in hospitals’ bottom lines, especially those in rural areas. It does this by increasing hospital revenue and reducing the high financial burden of uncompensated care that hospitals in states with large uninsured populations experience.

• This article was published at CEPR
• Acknowledgments: Thank you to Eileen Applebaum for providing valuable research insights and suggestions.

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1. See (as examples): Adam J. Singer et al., “US Emergency Department Visits and Hospital Discharges Among Uninsured Patients Before and After Implementation of the Affordable Care Act,” JAMA Network Open 2, no. 4 (2019),https://doi.org/10.1001/jamanetworkopen.2019.2662; Loredana Santo et al., “Trends in Emergency Department Visits Among People Younger Than Age 65 by Insurance Status: United States, 2010-2021,” National Health Statistics Reports, no. 197 (January 2024): 1–15, https://www.cdc.gov/nchs/data/nhsr/nhsr197.pdf.
2. Santo et al., 2024 (see Endnote 1).
3. Santo et al., 2024.
4. See: Madeline Guth et al., The Effects of Medicaid Expansion under the ACA: Studies from January 2014 to January 2020, Kaiser Family Foundation (KFF) (2020), 1–100,https://www.kff.org/affordable-care-act/the-effects-of-medicaid-expansion-under-the-aca-updated-findings-from-a-literature-review/; Fan Zhao and Roch A. Nianogo, “Medicaid Expansion’s Impact on Emergency Department Use by State and Payer,” Value in Health: The Journal of the International Society for Pharmacoeconomics and Outcomes Research 25, no. 4 (2022): 630–37, https://doi.org/10.1016/j.jval.2021.09.014.
5. Zhao and Nianogo, 2022 (see Endnote 4).
6. Afsaneh Asgharian et al., “Association Between the Affordable Care Act and Emergency Department Visits for Psychiatric Disease,” Western Journal of Emergency Medicine 24, no. 3 (2023): 447–53, https://doi.org/10.5811/westjem.57630.
7. Theodoros V. Giannouchos et al., “Association of Medicaid Expansion With Emergency Department Visits by Medical Urgency,” JAMA Network Open 5, no. 6 (2022): e2216913,https://doi.org/10.1001/jamanetworkopen.2022.16913.
8. David Dranove et al., “Uncompensated Care Decreased At Hospitals In Medicaid Expansion States But Not At Hospitals In Nonexpansion States,” Health Affairs 35, no. 8 (2016): 1471–79, https://doi.org/10.1377/hlthaff.2015.1344.
9. David Dranove et al., “The Impact of the ACA’s Medicaid Expansion on Hospitals’ Uncompensated Care Burden and the Potential Effects of Repeal,” Commonwealth Fund (2017), 1–9,https://www.commonwealthfund.org/sites/default/files/documents/___media_files_publications_issue_brief_2017_may_dranove_aca_medicaid_expansion_hospital_uncomp_care_ib.pdf.
10. Jordan H. Rhodes et al., “Heterogeneous Effects of the ACA Medicaid Expansion on Hospital Financial Outcomes,” Contemporary Economic Policy 38, no. 1 (2020): 81–93,https://doi.org/10.1111/coep.12428.
11. Fredric Blavin and Christal Ramos, “Medicaid Expansion: Effects On Hospital Finances And Implications For Hospitals Facing COVID-19 Challenges,” Health Affairs 40, no. 1 (2021): 82–90, https://doi.org/10.1377/hlthaff.2020.00502.
12. Gary J. Young et al., “Impact of ACA Medicaid Expansion on Hospitals’ Financial Status,” Journal of Healthcare Management 64, no. 2 (2019): 91, https://doi.org/10.1097/JHM-D-17-00177.
13. Meghana Ammula and Madeline Guth, What Does the Recent Literature Say About Medicaid Expansion?: Economic Impacts on Providers, Kellogg Family Foundation (2023), https://www.kff.org/affordable-care-act/what-does-the-recent-literature-say-about-medicaid-expansion-economic-impacts-on-providers/.
14. Joseph A. Benitez and Eric E. Seiber, “US Health Care Reform and Rural America: Results From the ACA’s Medicaid Expansions,” The Journal of Rural Health 34, no. 2 (2018): 213–22, https://doi.org/10.1111/jrh.12284.
15. Emmaline Keesee et al., “Uncompensated Care Is Highest for Rural Hospitals, Particularly in Non-Expansion States,” Medical Care Research and Review 81, no. 2 (2024): 164–70, https://doi.org/10.1177/10775587231211366.
16. See: Thomas DeLeire et al., “Impact of Insurance Expansion on Hospital Uncompensated Care Costs in 2014,” U.S. Department of Health and Human Services – Office of the Assistant Secretary for Planning and Evaluation (2014),http://aspe.hhs.gov/health/reports/2014/uncompensatedcare/ib_uncompensatedcare.pdf; Danrove et al., 2016 (at Endnote 8); Rhodes et al., 2020 (at Endnote 10).
17. Susan Camilleri, “The ACA Medicaid Expansion, Disproportionate Share Hospitals, and Uncompensated Care,” Health Services Research 53, no. 3 (2017): 1562–80,https://doi.org/10.1111/1475-6773.12702.
18. Keith, Katie. “The American Rescue Plan Expands The ACA.” Health Affairs 40, no. 5 (2021): 696–97. https://doi.org/10.1377/hlthaff.2021.00597.
19. Centers for Medicare & Medicaid Services (CMS), “ARCHIVED: Unwinding and Returning to Regular Operations after COVID-19.” n.d., https://www.medicaid.gov/resources-for-states/coronavirus-disease-2019-covid-19/archived-unwinding-and-returning-regular-operations-after-covid-19.
20. Ali Swenson, “Health Subsidies Expire, Launching Millions of Americans into 2026 with Steep Insurance Hikes,” Politics, Associated Press (January 1, 2026),https://apnews.com/article/affordable-care-act-health-subsidies-expire-35060610e82ca3257821c53f2a34ecf6.
21. Fredric Blavin and Michael Simpson, “Changes in Health Care Spending and Uncompensated Care under Enhanced Tax Credit Expiration for Marketplace Coverage: Updated 2026 State and National Estimates,” Urban Institute (2025),https://www.urban.org/research/publication/changes-health-care-spending-and-uncompensated-care-under-enhanced-tax-credit.