October 1, 2023

The Milky Way's Mass is Much Lower Than We Thought (Source: Universe Today)
One way to determine a galaxy’s mass is by looking at what’s known as its rotation curve. Measure the speed of stars in a galaxy versus their distance from the galactic center. The speed at which a star orbits is proportional to the amount of mass within its orbit, so from a galaxy’s rotation curve you can map the function of mass per radius and get a good idea of its total mass. We’ve measured the rotation curves for several nearby galaxies such as Andromeda, so we know the masses of many galaxies quite accurately.

But since we are in the Milky Way itself, we don’t have a great view of stars throughout the galaxy. Toward the center of the galaxy, there is so much gas and dust we can’t even see stars on the far side. So instead we measure the rotation curve using neutral hydrogen, which emits faint light with a wavelength of about 21 centimeters. This isn’t as accurate as stellar measurements, but it has given us a rough idea of our galaxy’s mass. We’ve also looked at the motions of the globular clusters that orbit in the halo of the Milky Way. From these observations, our best estimate of the mass of the Milky Way is about a trillion solar masses, give or take.

A new study is based on the third data release of the Gaia spacecraft. It contains the positions of more than 1.8 billion stars and the motions of more than 1.5 billion stars. While this is only a fraction of the estimated 100-400 billion stars in our galaxy, it is a large enough number to calculate an accurate rotation curve. What they found was surprising. The best fit to their data placed the mass at about 200 billion solar masses, which is a fifth of previous estimates. The absolute upper mass limit for the Milky Way is 540 billion, meaning that the Milky Way is at least half as massive as we thought. (9/30)

Nova, Supernova, Hypernova, Kilonova – What's The Difference? (Source: IFL Science)
Since we have learned more about the distances to these objects, and therefore their intrinsic brightnesses, we’ve created different categories. We classify the object Tycho saw as a supernova and use nova to refer to something a little different. Supernovas are not just slightly brighter versions of novas, they’re the result of one of two processes, each distinct from those that cause nova. Moreover, their intrinsic brightness differs by more than 10,000 times. Both classes of objects, and the more recently named hypernovas and kilonovas, have become among our best guides to the workings of the universe, so it is important to understand the nature of each. Click here. (9/30)

The Commercialization of Space is Here. International Law Isn't Prepared (Source: Slate)
Aspiring space nations, such as Luxembourg, India, and China, together with new categories of nonstate actors, including large industrial players, startups, and universities, raise questions about how we should regulate space. Explosive commercialization is particularly challenging for existing space law, whose foundations were set in the 1960s and designed with national governments in mind. Click here. (9/30)

China-India Rivalry Playing Out on the Moon (Source: Asia Times)
China will send an unmanned spacecraft to the south pole of the moon next year with the lunar aim of bringing two kilograms of rock samples back to Earth. CNSA said on Sep. 29 it will send Chang’e-6 to the far side of the moon, which has not yet been explored by scientists. It said it will launch a satellite called Queqiao 2, or Magpie Bridge 2, to relay communications to and from the moon in early 2024. Some commentators said that India, despite some earlier reports, cannot credibly claim to have reached the lunar south pole and that China has a chance to be a pioneer in that regard. (9/30)

Rivada Gains New Partner in US Space Force Satellite Project (Source; Business Post)
Rivada Networks has struck a partnership which will help it to provide satellite services to the US Space Force. Rivada plans to build a 600-satellite telecommunications constellation to host a global broadband network to rival Starlink and Kuiper Systems. Rivada said it was partnering with Artel LLC, which describes itself as a provider of secure network communication services to US government agencies. (9/30)

Labor Force Affected Space Command's Plight (Source: The Gazette)
The stress of uprooting lives. Reportedly, that is the real and tactical reason President Joe Biden and his Pentagon advisers chose Colorado Springs as the permanent home of Space Command. The command has been a political football since Donald Trump, in his final days as president, ordered it moved from Colorado Springs to Huntsville. As it turns out, the most strategic consideration was retaining qualified and seasoned talent for the sake of immediate readiness.

When any employer moves, public or private, civilian employees ask themselves: Is this job worth moving for? Moving means leaving behind friends, adult children and grandchildren who might live nearby. It could mean uprooting a child who is halfway through high school. It means selling a home, packing everything into a truck and finding a new home. Moving poses high-level stress on anyone. (10/1)

OSIRIS-APEX Aims for New Asteroid Target (Source: CNN)
The newly renamed OSIRIS-APEX mission is setting a course for Apophis, an asteroid with a fear-inducing reputation. The space rock — named for the Egyptian god of chaos and darkness — was once considered to be one of the most potentially hazardous asteroid threats to Earth. Apophis will come so close to Earth in 2029 that people will be able to see it with the naked eye. And that’s when OSIRIS-APEX will make its move, going into orbit around Apophis and studying it for 18 months. The spacecraft is no longer capable of collecting a sample, but it will use thrusters to kick up dust and rocks to study Apophis’ stony surface. (9/30)

Maybe in Your Lifetime, People Will Live on the Moon and Then Mars (Source: New York Times)
NASA will blast a 3-D printer up to the moon and then build structures, layer by additive layer, out of a specialized lunar concrete created from the rock chips, mineral fragments and dust that sits on the top layer of the moon’s cratered surface and billows in poisonous clouds whenever disturbed — a moonshot of a plan made possible through new technology and partnerships with universities and private companies. (10/1)