What Does the Milky Way Weigh? Hubble and Gaia Investigate

This illustration shows the fundamental architecture of our island city of stars, the Milky Way galaxy: a spiral disk, central bulge, and diffuse halo of stars and globular star clusters. Not shown is the vast halo of dark matter surrounding our galaxy.

We can’t put the whole Milky Way on a scale, but astronomers have been able to come up with one of the most accurate measurements yet of our galaxy’s mass, using NASA’s Hubble Space Telescope and the European Space Agency’s Gaia satellite.

The Milky Way weighs in at about 1.5 trillion solar masses (one solar mass is the mass of our Sun), according to the latest measurements. Only a tiny percentage of this is attributed to the approximately 200 billion stars in the Milky Way and includes a 4-million-solar-mass supermassive black hole at the center. Most of the rest of the mass is locked up in dark matter, an invisible and mysterious substance that acts like scaffolding throughout the universe and keeps the stars in their galaxies.

Earlier research dating back several decades used a variety of observational techniques that provided estimates for our galaxy’s mass ranging between 500 billion to 3 trillion solar masses. The improved measurement is near the middle of this range.

“We want to know the mass of the Milky Way more accurately so that we can put it into a cosmological context and compare it to simulations of galaxies in the evolving universe,” said Roeland van der Marel of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. “Not knowing the precise mass of the Milky Way presents a problem for a lot of cosmological questions.”


On the left is a Hubble Space Telescope image of a portion of the globular star cluster NGC 5466. On the right, Hubble images taken ten years apart were compared to clock the cluster’s velocity. A grid in the background helps to illustrate the stellar motion in the foreground cluster (located 52,000 light-years away). Notice that background galaxies (top right of center, bottom left of center) do not appear to move because they are so much farther away, many millions of light-years. 

The new mass estimate puts our galaxy on the beefier side, compared to other galaxies in the universe. The lightest galaxies are around a billion solar masses, while the heaviest are 30 trillion, or 30,000 times more massive. The Milky Way’s mass of 1.5 trillion solar masses is fairly normal for a galaxy of its brightness.

Astronomers used Hubble and Gaia to measure the three-dimensional movement of globular star clusters — isolated spherical islands each containing hundreds of thousands of stars each that orbit the center of our galaxy.

Although we cannot see it, dark matter is the dominant form of matter in the universe, and it can be weighed through its influence on visible objects like the globular clusters. The more massive a galaxy, the faster its globular clusters move under the pull of gravity. Most previous measurements have been along the line of sight to globular clusters, so astronomers know the speed at which a globular cluster is approaching or receding from Earth. However, Hubble and Gaia record the sideways motion of the globular clusters, from which a more reliable speed (and therefore gravitational acceleration) can be calculated.

The Hubble and Gaia observations are complementary. Gaia was exclusively designed to create a precise three-dimensional map of astronomical objects throughout the Milky Way and track their motions. It made exacting all-sky measurements that include many globular clusters. Hubble has a smaller field of view, but it can measure fainter stars and therefore reach more distant clusters. The new study augmented Gaia measurements for 34 globular clusters out to 65,000 light-years, with Hubble measurements of 12 clusters out to 130,000 light-years that were obtained from images taken over a 10-year period.

When the Gaia and Hubble measurements are combined as anchor points, like pins on a map, astronomers can estimate the distribution of the Milky Way’s mass out to nearly 1 million light-years from Earth.

“We know from cosmological simulations what the distribution of mass in the galaxies should look like, so we can calculate how accurate this extrapolation is for the Milky Way,” said Laura Watkins of the European Southern Observatory in Garching, Germany, lead author of the combined Hubble and Gaia study, to be published in The Astrophysical Journal. These calculations based on the precise measurements of globular cluster motion from Gaia and Hubble enabled the researchers to pin down the mass of the entire Milky Way.

The earliest homesteaders of the Milky Way, globular clusters contain the oldest known stars, dating back to a few hundred million years after the big bang, the event that created the universe. They formed prior to the construction of the Milky Way’s spiral disk, where our Sun and solar system reside.

“Because of their great distances, globular star clusters are some of the best tracers astronomers have to measure the mass of the vast envelope of dark matter surrounding our galaxy far beyond the spiral disk of stars,” said Tony Sohn of STScI, who led the Hubble measurements.

The international team of astronomers in this study are Laura Watkins (European Southern Observatory, Garching, Germany), Roeland van der Marel (Space Telescope Science Institute, and Johns Hopkins University Center for Astrophysical Sciences, Baltimore, Maryland), Sangmo Tony Sohn (Space Telescope Science Institute, Baltimore, Maryland), and N. Wyn Evans (University of Cambridge, Cambridge, United Kingdom).

Having a Quarter-Life Crisis? How to Make Life Better for Future You

“You’ve got your whole life ahead of you,” young adults are often told—but that’s of little comfort to the many 20- and 30-somethings who face “adulting” challenges like career uncertainty, overwhelming student loan debt, and relationship difficulties. The uncertainties of this time of life leave many feeling depressed, insecure, and rudderless. The good news is that you’re not alone—there’s a name for this experience: the quarter-life crisis.

“During their early 20s to early 30s young adults may feel either ill-prepared for or trapped by adult roles,” explains Jacob Tebes, PhD, who is a professor of psychiatry (psychology) at Yale School of Medicine and at the Yale Child Study Center. “This may trigger a quarter-life crisis that leads to heightened feelings of stress, as well as anxiety or depression.”

Like the better-known midlife crisis, the quarter-life crisis is common—one survey suggests that as many as 70 percent of young adults have them.

“Young adulthood is more challenging than ever, especially when making choices,” explains Dr. Tebes. “The amount of information available in our hyper-connected world makes it very easy to second-guess yourself. Part of the problem is the growing belief that there is a ‘best’ choice to be made—about your relationships, career, commitments, or even downtime. This is an illusion,” he says. “There is no ‘best choice.’ It is what we do after we choose that makes all the difference in how something works out, even when initially things may not turn out so well.”

One good choice you can make, though, is to take care of yourself. Our Yale Medicine doctors discuss health matters to consider as you reach the quarter-life milestone.

Even social drinking can lead to liver cirrhosis.

It’s a common misconception that only people who have been heavy drinkers for decades have to worry about alcohol-related cirrhosis of the liver, a chronic condition in which the organ sustains permanent scarring and impaired function. “The amount of liver cirrhosis we are detecting in young people is increasing dramatically,” says Yale Medicine hepatologist Michael Nathanson, MD. “It’s the most quickly growing group of people dying of cirrhosis in this country.”

Rates of liver cirrhosis deaths from all causes, including hepatitis C, have skyrocketed in the United States in the last two decades, increasing by 65 percent overall for all age groups between 1999 and 2016. The sharpest increase, though, was among young adults, ages 25 to 34. Deaths from liver cirrhosis in this age group rose nearly 11 percent per year, according to The BMJ, which attributes the increase entirely to drinking.

“Certainly, some of the patients we see in their 20s and 30s think they are just drinking socially or because of stresses, and they don’t understand the damage they are doing to their livers and how the damage accumulates quickly,” says Dr. Nathanson. “Drinking, even at their age, could lead to serious health problems and even death, and it isn’t going to take 10, 20, or 30 years in all cases.”

Don’t assume your body will tell you that you’ve had enough, cautions Dr. Nathanson. He often sees patients who had no idea that their social drinking was harmful until the problem became serious. (Early stage liver disease has no symptoms.) He also reminds quarter-lifers that alcohol use in general is one of the leading causes of death (for a variety of reasons, including accidents) and disability for their age bracket.

While Department of Health and Human Services guidelines define moderate drinking as one drink a day for women and two drinks a day for men, the safest course of action is to abstain from drinking altogether. If you take medications (prescription or over-the-counter drugs), ask your doctor or pharmacist about alcohol consumption while on them since many, including acetaminophen, can hypersensitize your liver to the effects of alcohol, Dr. Nathanson explains.

More millennials are being diagnosed with colorectal cancer.

People tend to think that colon and rectal cancers (colorectal cancers) only happen to older adults. But there is a disturbing and ongoing trend of young people being diagnosed with these cancers.

“Colorectal cancer is clearly on the rise in the younger generations,” says Hulda Einarsdottir, MD, a Yale Medicine colorectal surgeon. Research has found that people born in 1990—who will be 29 years old this year—have double the risk of colon cancer and quadruple the risk of rectal cancer compared to people born around 1950. Researchers are still trying to figure out why.

With this in mind, one thing you can do is be aware of symptoms that you should discuss with your doctor. “Even if you’re in your teens or 20s,” Dr. Einarsdottir says, “if you have rectal bleeding, if you have any change in your bowel habits, any change in appetite (like feeling “full” early), weight loss, or abdominal pain that is not explained, you should get checked out.”

Rectal bleeding can be misunderstood, Dr. Einarsdottir adds. “I get a lot of patients referred for hemorrhoids. But even in a young patient, you have to make sure that it’s not something more serious,” she says. In certain cases, she may recommend a colonoscopy, the screening test that is used to identify and remove colorectal cancers and precancers.

Using SPF now may help you avoid skin cancer later.

“It is difficult to convince 20-somethings that the tans they bring back from their Caribbean vacations might lead to skin cancer in 30 years,” says dermatologist Kathleen Cook Suozzi, MD, aesthetic director at Yale Medicine Dermatology. According to the American Academy of Dermatology, melanoma is the second most common form of cancer in women under 30.

“Whenever I see a patient younger than 45 for skin cancer surgery,” Dr. Suozzi says, “I ask about their history of tanning bed use, and the correlation is very strong. Recently, state laws have limited minors’ access to tanning beds, and further education about the effects of ultraviolet [UV] damage from indoor or outdoor tanning will hopefully help halt this sobering trend.”

Protecting your youthful appearance can be another motivation to use sunscreen. “The sun damage sustained now will add years to the skin’s apparent age in your 40s,” Dr. Suozzi says. In addition to sunspots, skin conditions like rosacea and melasma are brought on or worsened by UV damage. “While there are lasers and chemical peels to help improve the look of sun-damaged skin, it is much more difficult to erase damage than it is to prevent it,” she says.

Start thinking about your future family.

Having kids may be the furthest thing from your mind right now. “In your 20s, you may be doing everything you can to not get pregnant,” says reproductive endocrinologist David Seifer, MD. “Then in your mid-30s, it’s like a role reversal.”

“For women, fertility is not just an on/off switch,” Dr. Seifer says. “It’s going to be a gradual decline for every woman on the planet.” Sometime around age 37 to 38, “your fertility declines at an accelerated rate. So, it’s important to be conscious of that.”

He advises that young women think about at what point they might consider having children and how many they want to have. “People just think about timing the first one, but sometimes it can be the second or third when things get more difficult,” he says. Dr. Seifer also suggests that women ask their female relatives when menopause started for them.

“Generally, if your mother or your sister went through menopause before the age of 50, you may be genetically predisposed to going through menopause at an earlier age. That itself should probably be one small indication that you might consider having your family earlier than later,” he says.

Even if becoming a parent seems far off now, women and men should be aware of risk factors that can deplete fertility—such as smoking, sexually transmitted diseases, stress, and obesity—and make healthy lifestyle changes as needed.

While young men aren’t under the same time pressure as young women, they should know that sperm quality deteriorates over time, says Yale Medicine urologist Daniel Kellner, MD.

One immediate step young men can take is to avoid steroid use. If you’ve taken them at any point or have been prescribed testosterone for low-testosterone, either can affect sperm quality temporarily—or even permanently, Dr. Kellner says. Heavy alcohol or drug use all negatively impact sperm quality and count, and can even interrupt the brain hormones that control sperm production.

If the time isn’t right, you don’t have to rush, though. It is possible to preserve eggs, embryos, and sperm if you would rather have children in your 40s or 50s—or if you have a health condition such as cancer in which treatment can affect fertility.

Just be mindful that “there is a biological clock—it’s real,” says Dr. Seifer. He recommends those who are delaying having children beyond their mid-30s consider testing (bloodwork and an ultrasound), which can provide a snapshot of your overall fertility.

Make annual check-ups with your doctor.

“While these young adults are among the healthiest age groups, they should get in the habit of having good preventive health care,” says Yale Medicine’s Xavier Llor, MD, medical director of the Smilow Screening & Prevention Program. That means seeing a doctor annually for a check-up and to discuss screening tests that are recommended for their age bracket. According to Dr. Llor, young adults in their mid-20s and 30s should talk to their health care providers about health risks such as tobacco and alcohol use, sun exposure, diet and nutrition, physical exercise, weight, environmental and occupational exposures, and family history. He also recommends that women have pelvic exams and Pap smears every three years starting at age 21 to check for cervical cancer.

In short, find a health care provider you trust, and make (and keep) annual appointments. “It’s tempting to just go to the doctor when you have a sore throat, but the best way to stay healthy at this time of life is good preventive care so if symptoms do crop up, they can be addressed early,” Dr. Llor says.

Good health, they say, is the foundation of success in life. So, as you work through this quarter-life phase, take care of yourself to ensure that the decades ahead are ­­­­­­­yours for the taking.

Sorry Hollywood, it’s Going to Take a Lot More to Destroy an Asteroid

A frame-by-frame showing how gravity causes asteroid fragments to reaccumulate in the hours following impact. 

It’s become something of an action movie cliche: an asteroid is hurling towards Earth, its impact will cause a mass extinction, and the only hope for humanity is a ragtag group of astronauts and average Joes who will fly to the asteroid and blow it to pieces using nukes. The idea has been explored so many times by Hollywood that it seems like this is actually something space agencies have planned.

And in truth, they are, though the execution may be a little more sophisticated. For decades, space agencies have considered various methods for destroying asteroids that threaten Earth. But according to a new study led by researchers from John Hopkins University, incoming asteroids may be harder to break apart than we thought.

The study, which recently appeared online and is awaiting publication in the March 15th issue of Icarus, was led by Charles El Mir – a recent PhD graduate from the JHU Department of Mechanical Engineering. He was joined by K.T. Ramesh (the director of the Hopkins Extreme Materials Institute) and Derek Richardson, a professor of astronomy at the University of Maryland.

For the sake of their study, the team relied on a new understanding of how rocks fracture combined with a new method of computer modeling to simulate asteroid collisions. As El Mir described in a recent JHU press release, what they found was rather surprising:

“We used to believe that the larger the object, the more easily it would break, because bigger objects are more likely to have flaws. Our findings, however, show that asteroids are stronger than we used to think and require more energy to be completely shattered.”

One of the problems of knowing how an asteroid would respond to any attempt to blow it up has to do with scale. While scientists understand how rocks behave on smaller scales (such as hand-sized stones or boulders), city-sized objects like a Near-Earth Asteroid (NEA) present a whole different set of challenges.

In the early 2000s, another team of researchers had created a computer model to determine what kind of impacts were necessary to destroy an asteroid. Based on factors like mass, temperature, and composition, they determined that an asteroid that was 1 km (0.62 mi) in diameter would need to strike an asteroid 25 km (15.5 mi) in diameter at a velocity of no less than 500 km/s (310 mps) to destroy it.

For their study, El Mir and his colleagues entered the same scenario into a new computer model called the Tonge-Ramesh model, named in part for co-author K.T. Ramesh who helped create it. This model is able to account for more detailed, smaller-scale processes that occur during an asteroid collision – such as the limited speed of cracks in the asteroids

The simulation they then ran occurred in two phases – a short-term fragmenting phase that covers the first few seconds after the impact followed by long-term re-absorption phase where gravitational forces pull the fragments back together over the course of hours. What they found was that the initial impact formed a crater and caused millions of cracks to form and propagate through the asteroid.

However, contrary to what was previously thought, the impact didn’t result in the destruction of the asteroid. Instead, the propagated cracks reached all the way to core, which then exerted a strong gravitational pull on the fragments during the second phase of the simulation. In the end, the asteroid managed to retain its integrity and the fragments that broke loose were merely redistributed over the damaged core. As El Mir explained:

“It may sound like science fiction but a great deal of research considers asteroid collisions. For example, if there’s an asteroid coming at earth, are we better off breaking it into small pieces, or nudging it to go a different direction? And if the latter, how much force should we hit it with to move it away without causing it to break? These are actual questions under consideration.”

This study could go a long way towards informing future asteroid-impact mitigation strategies. By knowing what kinds of impactors and forces are not sufficient for breaking up an asteroid, mission planners will have accurate parameters to work with. This knowledge could also have extensive applications with asteroid mining, letting drillers know exactly how asteroids of various sizes will respond to drilling and extraction from.

And as Ramesh indicated, this information will have all kinds of practical uses that can’t come soon enough:

“We are impacted fairly often by small asteroids, such as in the Chelyabinsk event a few years ago. It is only a matter of time before these questions go from being academic to defining our response to a major threat. We need to have a good idea of what we should do when that time comes – and scientific efforts like this one are critical to help us make those decisions.”

In sum, humanity is not doomed in the event that an asteroid starts hurtling towards Earth, just better informed. And that will go a long towards making sure we remain safe from major impacts in the future. As an added bonus, now when Hollywood decides to do another disaster movie featuring an asteroid, they’ll be able to get the physics right!

Gotcha! Scientists fingerprint proteins using their vibrations

In the cells of every living organism — humans, birds, bees, roses and even bacteria — proteins vibrate with microscopic motions that help them perform vital tasks ranging from cell repair to photosynthesis.

These life-giving tremors are the topic of a study published in Nature Communications.

A team led by University at Buffalo physicist Andrea Markelz reports that it has developed a method for rapidly measuring proteins’ unique vibrations.

The advance could open new possibilities in biological research, such as studying the microscopic motions of proteins more efficiently, or leveraging vibrational patterns as “fingerprints” to quickly determine whether specific proteins are present in a laboratory sample.

Scientists could also use the new technique to swiftly assess whether pharmaceuticals designed to inhibit a protein’s vibrations are working. This would require comparing the vibrational signatures of proteins before and after the application of inhibitors.

“Proteins are elegant and robust nanomachines that nature has developed,” says Markelz, PhD, a professor of physics in the UB College of Arts and Sciences. “We know nature uses molecular motions to optimize these machines. By learning the underlying principles of this optimization, we can develop new biotechnology for medicine, energy harvesting and even electronics.”

Katherine A. Niessen, PhD, a UB researcher who is now a development scientist at Corning, is first author of the paper, which includes contributions from scientists in the UB Department of Physics, the UB Department of Structural Biology in the Jacobs School of Medicine and Biomedical Sciences at UB, the Hauptman-Woodward Medical Research Institute, the National Heart, Lung, and Blood Institute and the University of Wisconsin-Milwaukee. The work was funded by the National Science Foundation and U.S. Department of Energy.

Measuring protein vibrations more quickly

Markelz is a leading expert on the study of protein vibrations. These movements enable proteins to change shape quickly so they can readily bind to other proteins — a process that’s critical to normal biological function.

Several years ago, Markelz’ lab developed a technique called anisotropic terahertz microscopy (ATM) to observe protein vibrations in detail, including the energy and direction of movements.

In ATM, researchers shine terahertz light on a molecule. Then, they measure the frequencies of light the molecule absorbs. This provides insight into the molecules’ motion because molecules vibrate at the same frequency as the light they soak up.

The new study in Nature Communications reports that Markelz’ team has improved upon ATM by overcoming one of the method’s limitations: The need to painstakingly rotate and re-center protein samples several times in a microscope to gather enough useful data.

Now, “instead of rotating the protein sample, we rotate the polarization of the light we shine on the sample,” Markelz says. With this adjustment, it takes just 4 hours to make useful measurements — six times faster than before. The new technique also generates more detailed data.

A sensitive ‘fingerprinting’ technique

Using the new approach, Markelz and colleagues measured the vibrations of four different proteins, generating a recognizable vibrational “fingerprint” for each that consisted of the molecule’s unique light absorption pattern.

The proteins studied were chicken egg-white lysozyme (a well-researched protein in the field), photoactive yellow proteins (thought to help protect certain photosynthesizing bacteria from ultraviolet light), dihydrofolate reductase (a drug target for antibiotics and cancer), and RNA G-quadruplexes (thought to be involved in vital cellular functions such as gene expression).

The new method produced distinct light-absorption spectra for chicken egg-white lysozymes that were freely moving versus chicken egg-white lysozymes that were bound by a compound that inhibits the lysozymes’ function — and alters their vibrations. This demonstrates the technique’s utility in quickly identifying the presence of a working inhibitor.