NASA Astronomy Picture of the Day

Apr 14 2023

Portrait of NGC 3628

Sharp telescopic views of NGC 3628 show a puffy galactic disk divided by dark dust lanes. Of course, this portrait of the magnificent, edge-on spiral galaxy puts some astronomers in mind of its popular moniker, the Hamburger Galaxy. It also reveals a small galaxy nearby (below), likely a satellite of NGC 3628, and a very faint but extensive tidal tail. The drawn out tail stretches for about 300,000 light-years, even beyond the left edge of the frame. NGC 3628 shares its neighborhood in the local universe with two other large spirals M65 and M66 in a grouping otherwise known as the Leo Triplet. Gravitational interactions with its cosmic neighbors are likely responsible for creating the tidal tail, as well as the extended flare and warp of this spiral's disk. The tantalizing island universe itself is about 100,000 light-years across and 35 million light-years away in the northern springtime constellation Leo.

https://apod.nasa.gov/apod/astropix.html?

European Space Agency, ESA - Juice launch to Jupiter

Apr 14, 2023

We’re going to Jupiter – and three of its moons! The Juice spacecraft is now securely fastened to an Ariane 5 rocket and ready for launch. Juice, for Jupiter Icy Moons Explorer, will explore Jupiter’s complex environment in depth after an eight-year journey. Follow all the action and learn more about the mission in this special programme co-produced by ESA and Arianespace. Lift-off is expected at 14:14 CEST and our presenters will be live all the way until confirmation of the deployment of the spacecraft’s solar arrays.

https://www.youtube.com/watch?v=MvHcGmQPcsI

https://www.esa.int/Science_Exploration/Space_Science/Juice

NASA’s Lucy Mission Snaps its First Views of Trojan Asteroid Targets

Apr 13, 2023

Some of the asteroids NASA’s Lucy mission will visit are still more than 330 million miles (530 million kilometers) away from the spacecraft, which is more than three times the average distance between Earth and the Sun. But despite the great distance and the comparatively small sizes of these asteroids, Lucy caught views of four of them recently.

From March 25 to 27, 2023, Lucy used its highest resolution imager, L’LORRI, to capture its first views of four Jupiter Trojan asteroids. From left to right in the above image: Eurybates, Polymele, Leucus, and Orus.

Although the four images are all at the same scale, the orientation of each is different, reflecting the different orientations of the L’LORRI camera as it turned to capture each target.

The targets were also observed for different time periods based on their rotation periods:

• Eurybates images were taken over a span of 6.5 hours.

• Polymele, about 2.5 hours.

• Leucus, 2 hours.

• Orus, 10 hours.

These images are the first in a series of planned observations designed to measure how the Trojan asteroids reflect light at higher angles than is observable from Earth. Though the asteroids are still just single points of light in these images, seen against a background of distant stars, the data will help the team choose exposure times for Lucy’s close-up observations of its targets.

Lucy will fly by these asteroids in 2027 and 2028 as the spacecraft travels through a swarm of small asteroids that lead Jupiter in its orbit around the Sun. Lucy is just more than a year into a 12-year voyage that entails close observation of nine of Jupiter’s Trojans — the first space mission ever to visit them — and two main belt asteroids.

https://www.nasa.gov/image-feature/goddard/2023/nasa-s-lucy-mission-snaps-its-first-views-of-trojan-asteroid-targets

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Giant Galaxy Seen in 3D by NASA's Hubble Space Telescope and Keck Observatory

Apr 13, 2023

Though we live in a vast three-dimensional universe, celestial objects seen through a telescope look flat because everything is so far away. Now for the first time, astronomers have measured the three-dimensional shape of one of the biggest and closest elliptical galaxies to us, M87. This galaxy turns out to be "triaxial," or potato-shaped. This stereo vision was made possible by combining the power of NASA's Hubble Space Telescope and the ground-based W. M. Keck Observatory on Maunakea, Hawaii.

In most cases, astronomers must use their intuition to figure out the true shapes of deep-space objects. For example, the whole class of huge galaxies called "ellipticals" look like blobs in pictures. Determining the true shape of giant elliptical galaxies will help astronomers understand better how large galaxies and their central large black holes form.

Scientists made the 3D plot by measuring the motions of stars that swarm around the galaxy's supermassive central black hole. The stellar motion was used to provide new insights into the shape of the galaxy and its rotation, and it also yielded a new measurement of the black hole's mass. Tracking the stellar speeds and position allowed researchers to build a three-dimensional view of the galaxy.

Astronomers at the University of California, Berkeley, were able to determine the mass of the black hole at the galaxy's core to a high precision, estimating it at 5.4 billion times the mass of the Sun. Hubble observations in 1995 first measured the M87 black hole as being 2.4 billion solar masses, which astronomers deduced by clocking the speed of the gas swirling around the black hole. When the Event Horizon Telescope, an international collaboration of ground-based telescopes, released the first-ever image of the same black hole in 2019, the size of its pitch-black event horizon allowed researchers to calculate a mass of 6.5 billion solar masses using Einstein's theory of general relativity.

The stereo model of M87 and the more precise mass of the central black hole could help astrophysicists learn the black hole's spin rate. "Now that we know the direction of the net rotation of stars in M87 and have an updated mass of the black hole, we can combine this information with data from the Event Horizon Telescope to constrain the spin," said Chung-Pei Ma, a UC Berkeley lead investigator on the research.

Over ten times the mass of the Milky Way, M87 probably grew from the merger of many other galaxies. That's likely the reason M87's central black hole is so large – it assimilated the central black holes of one or more galaxies it swallowed.

Ma, together with UC Berkeley graduate student Emily Liepold (lead author on the paper published in the Astrophysical Journal Letters) and Jonelle Walsh at Texas A&M University were able to determine the 3D shape of M87 thanks to a new precision instrument mounted on the Keck II Telescope. They pointed Keck at 62 adjacent locations of the galaxy, mapping out the spectra of stars over a region about 70,000 light-years across. This region spans the central 3,000 light-years where gravity is largely dominated by the supermassive black hole. Though the telescope cannot resolve individual stars because of M87's great distance, the spectra can reveal the range of velocities to calculate mass of the object they're orbiting.

"It's sort of like looking at a swarm of 100 billion bees," said Ma. "Though we are looking at them from a distance and can't discern individual bees, we are getting very detailed information about their collective velocities."

The researchers took the data between 2020 and 2022, as well as earlier star brightness measurements of M87 from Hubble, and compared them to computer model predictions of how stars move around the center of the triaxial-shaped galaxy. The best fit to this data allowed them to calculate the black hole's mass. "Knowing the 3D shape of the 'swarming bees' enabled us to obtain a more robust dynamical measurement of the mass of the central black hole that is governing the bees' orbiting velocities," said Ma.

In the 1920s, astronomer Edwin Hubble first classified galaxies according to their shapes. Flat disk spiral galaxies could be viewed from various projection angles of the sky: face-on, oblique, or edge-on. But the "blobby-looking" galaxies were more problematic to characterize. Hubble came up with the term elliptical. They could only be sorted out by how great the ellipticity was. They didn't have any apparent dust or gas inside of them for better distinguishing between them. Now, a century later astronomers have a stereoscopic look at a prototypical elliptical galaxy.

https://www.nasa.gov/feature/goddard/2023/giant-galaxy-seen-in-3d-by-nasas-hubble-space-telescope-and-keck-observatory

https://youtu.be/hZkEo5QMNr0

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