A Better Way to Look

K-type dwarf stars are dimmer than the Sun but brighter than faint stars. These stars live for a very long time, 17 to 70 billion years, compared to 10 billion years for the Sun. This gives plenty of time for life to evolve on any planets in their habitable zones. Also, they have less extreme activity in their youth than M-type stars (red dwarfs), the most common star type in the Milky Way Galaxy.

K-stars may be in a ‘sweet spot’ between Sun-analog stars and M-type stars astronomers at NASA’s Goddard Space Flight Center and writers of a paper published in the Astrophysical Journal Letters.

Scientists consider the simultaneous presence of oxygen and methane in a planet’s atmosphere to be a strong biosignature because these gases like to react with each other, destroying each other. So if they are present in an atmosphere together, that implies something is producing both of them quickly, quite possibly life.

However, because exoplanets are so remote, there needs to be significant amounts of oxygen and methane in an exoplanet’s atmosphere for it to be seen by observatories on Earth. The researchers found that the oxygen-methane biosignature is likely to be stronger around a K-type star than a Sun-like star.

This stronger oxygen-methane signal has also been predicted for planets around M-type stars, but their high activity levels might make M-stars unable to host habitable worlds. K-type stars can offer the advantage of a higher probability of simultaneous oxygen-methane detection compared to Sun-like stars without the disadvantages that come along with an M-star host.

Additionally, exoplanets around K-type stars will be easier to see than those around Sun-like stars simply because K-stars are dimmer. The Sun is 10 billion times brighter than an Earth-like planet around it. That’s a lot of light you have to suppress if you want to detect an orbiting planet. A K-star might be ‘only’ a billion times brighter than an Earth-like planet orbiting it.

The Milky Way is Really Big

The Milky Way Galaxy (the one we’re in) contains an estimated 200 billion stars. But that’s just the tip of the iceberg, the Galaxy is surrounded by vast amounts of an unknown material called “dark matter” (matter that we can’t normally detect because it doesn’t interact with the electromagnetic spectrum). Astronomers know it exists because, dynamically, the Milky Way would fly apart if dark matter didn’t keep a gravitational lid on things.

Image result for milky way galaxy

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Still, astronomers would like to have a more precise measure of the Galaxy’s total mass to better understand how the myriad galaxies throughout the Universe form and evolve. A team of researchers from ESO, the Space Telescope Science Institute, the Johns Hopkins University Center for Astrophysical Sciences, and the University of Cambridge combined observations from the NASA/ESA Hubble Space Telescope and ESA’s Gaia satellite to study the motions of globular star clusters that orbit our Galaxy. The faster the clusters move under the entire Galaxy’s gravitational pull, the more massive it is. The team concluded the Milky Way has an equivalent mass of 1.54 trillion solar masses, most of it locked up in dark matter.

This new mass estimate puts the Milky Way 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.

Previous estimates of the Milky Way’s mass ranged from 500 billion to 3 trillion solar masses. This huge margin of error arose primarily from the different methods used for measuring the distribution of dark matter, which makes up about 90% of the mass of the Galaxy.

Given the elusive nature of the dark matter, the team had to use a clever method to weigh the Milky Way, which relied on measuring the velocities of globular clusters, dense star clusters that orbit the spiral disk of the Galaxy at great distances.

The scientists used Gaia’s second data release, which includes measurements of globular clusters as far as 65,000 light-years from Earth, as a basis for the study.

Observations from Hubble allowed faint and distant globular clusters, as far as 130,000 light-years from Earth, to be added to the study. As Hubble has been observing some of these objects for a decade, it was possible to accurately track the velocities of these clusters as well.

By combining Gaia’s measurements with measurements from Hubble, the scientists could better pin down the Milky Way’s mass in a way that would be impossible without both space telescopes,

The team’s results will be published in the Astrophysical Journal.

Galactic Collision Now on Video

Scientists have long known that the nearby galaxy Andromeda and our own Milky Way galaxy will collide in four to five billion years, but now a new computer simulation from the International Centre for Radio Astronomy Research in Western Australia shows what the colossal crash may look like.

The simulation is part of new research showing that massive galaxies like Andromeda tend to grow by cannibalizing smaller galaxies.

This should be fun:

An article describing the research was published online in the Monthly Notices of the Royal Astronomical Society on September 18, 2014.