“The Fermi bubbles are enormous structures of hot gas that extend above and below the disk of the Milky Way, reaching about 25,000 light years in each direction from the galaxy’s center — spanning a total height of 50,000 light years,” says Rongmon Bordoloi, associate professor of physics at North Carolina State University and corresponding author of the research.

“Fermi bubbles are a relatively recent discovery — they were first identified by telescopes that ‘see’ gamma rays in 2010 — there are different theories about how it happened, but we do know that it was an extremely sudden and violent event, like a volcanic eruption but on a massive scale.”

Bordoloi and the research team used the U.S. National Science Foundation Green Bank Telescope (NSF GBT) to observe the Fermi bubbles and get high resolution data about the composition of the gas within and the speed at which it is moving. These measurements were twice as sensitive as previous radio telescope surveys of the Fermi bubbles and allowed them to observe finer detail within the bubbles.

Most of the gas inside the Fermi bubbles is around 1 million degrees Kelvin. However, the research team also found something surprising: dense clouds of neutral hydrogen gas, each one measuring several thousand solar masses, dotted within the bubbles 12,000 light years above the center of the Milky Way.

“These clouds of neutral hydrogen are cold, relative to the rest of the Fermi bubble,” says Andrew Fox, ESA-AURA Astronomer at the Space Telescope Science Institute and coauthor of the paper.

“They’re around 10,000 degrees Kelvin, so cooler than their surroundings by at least a factor of 100. Finding those clouds within the Fermi bubble is like finding ice cubes in a volcano.”

Their existence is surprising because the hot (over 1 million degrees Kelvin), high-velocity environment of the nuclear outflow should have rapidly destroyed any cooler gas.

“Computer models of cool gas interacting with hot outflowing gas in extreme environments like the Fermi bubbles show that cool clouds should be rapidly destroyed, usually within a few million years, a timescale that aligns with independent estimates of the Fermi bubbles’ age,” Bordoloi says. “It wouldn’t be possible for the clouds to be present at all if the Fermi bubbles were 10 million years old or older.

“What makes this discovery even more remarkable is its synergy with ultraviolet observations from the Hubble Space Telescope (HST),” Bordoloi says. “The clouds lie along a sightline previously observed with HST, which detected highly ionized multiphase gas, ranging in temperatures from a million to 100,000 Kelvin — which is what you’d expect to see if a cold gas is getting evaporated.”

The team was also able to calculate the speed at which the gases are moving, which further confirmed the age.

“These gases are moving around a million miles per hour, which also marks the Fermi bubbles as a recent development,” Bordoloi says. “These clouds weren’t here when dinosaurs roamed Earth. In cosmic time scales, a million years is the blink of an eye.”

“We believe that these cold clouds were swept up from the Milky Way’s center and carried aloft by the very hot wind that formed the Fermi bubbles,” says Jay Lockman, an astronomer at the Green Bank Observatory and coauthor of the paper. “Just as you can’t see the motion of the wind on Earth unless there are clouds to track it, we can’t see the hot wind from the Milky Way but can detect radio emission from the cold clouds it carries along.”

This discovery challenges current understanding of how cold clouds can survive the extreme energetic environment of the Galactic Center, placing strong empirical constraints on how outflows interact with their surroundings. The findings provide a crucial benchmark for simulations of galactic feedback and evolution, reshaping our view of how energy and matter cycle through galaxies.

The work appears in Astrophysical Journal Letters and is supported by the National Science Foundation under grant number AST-2206853.

“We found that patients not only maintained their weight loss after abdominoplasty, but also continued to lose weight over time – up to ten pounds, on average,” comments senior author John Y.S. Kim of Northwestern University Feinberg School of Medicine, Chicago. “This postoperative weight loss appears greater, and increases at later follow-up times, in patients with initially higher body mass index [BMI].”

Continued weight loss up to five years after tummy tuck

Abdominoplasty is a cosmetic surgical procedure to improve the appearance of the abdomen. In 2023, ASPS Member Surgeons performed more than 170,000 abdominoplasties, according to ASPS statistics. Many of these procedures are performed in patients with massive weight loss that leaves them with excess, sagging skin.

Plastic surgeons have observed that patients may continue to lose weight after abdominoplasty. However, there is little research evidence on this issue, including whether the abdominoplasty procedure itself contributes to long-term weight loss.

Dr. Kim and colleagues performed a study to assess changes in body weight in 188 patients who underwent abdominoplasty between 2018 and 2022. Ninety-seven percent of patients were women. The average preoperative weight was about 168 pounds with a BMI of 27.7. Most patients underwent liposuction or a further procedure to remove excess fat (lipectomy) at the same time as abdominoplasty. Trends in body weight were assessed through up to five years after surgery.

The results showed continued weight loss after abdominoplasty. At three to six months, average weight loss was between five and six pounds, with about a three percent decrease in BMI. From one to four years, weight loss was about five pounds, for a BMI reduction of about two percent. By five years (in a limited number of patients), average weight loss was nearly ten pounds, with more than a five percent decrease in BMI.

‘Near-constant negative change in body weight’ after abdominoplasty

Overall, about 60% of patients lost weight during follow-up. Further analysis showed a “near constant negative change in body weight that did not significantly change over time,” the researchers write.

After adjustment for other factors, continued weight loss was more likely for older patients, for those who underwent liposuction/lipectomy, and those who had never smoked. Weight loss was greater for patients who had higher body weight and BMI before surgery, and for a small number of patients who used the newer weight loss medication semaglutide.

The study adds new evidence that “post-abdominoplasty weight reduction is a quantifiable phenomenon and that patients undergoing abdominoplasty continue to lose a significant amount of weight for up to five years after surgery,” the researchers write. They note some key limitations of their study, including varying follow-up times and potential confounding factors.

The study cannot definitively explain why patients continue to lose weight after surgery. However, Dr. Kim and coauthors write, “We have found that patients who were able to achieve weight loss after their abdominoplasty succeeded in developing healthy habits that centered around nutrition and exercise.” They highlight the need for an “evidence-based platform” to assess weight changes after abdominoplasty and to identify factors associated with long-term weight loss.