Saturday, March 9, 2024

Barred Spiral Galaxy NGC 1808

Barred Spiral Galaxy NGC 1808
Click the image for higher resolution (2.9 MB)

NGC 1808 is a barred spiral galaxy located in the southern constellation Columba (the dove). This image was captured using the Dark Energy Camera (DECam), which is mounted on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), a Program of NSF's NOIRLab, in Chile. The core of NGC 1808 is thought to house a supermassive black hole, characterized by its accretion of material and higher-than-normal brightness. The smoldering center is closely surrounded by a faint blue ring populated with star clusters and supernova remnants. This region is defined by its starburst activity, producing an exceptional number of hot, bright, young stars. The abundance of rapid star formation is thought to be the result of past tidal interactions with the nearby galaxy NGC 1792. Laced throughout this middle region of NGC 1808 are dark dust lanes resulting from large outflows of hydrogen gas from the galactic nucleus. The softly glowing outer arms surrounding the galaxy are slightly warped, again pointing to tidal interactions with NGC 1792. Such an interaction could have created the asymmetrical shape of NGC 1808 and hurled gas towards the nucleus, igniting the rapid star formation in its surrounding ring.
Image Credit: Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA
Image processing: R. Colombari and M. Zamani (NSF's NOIRLab)
Image enhancement: Jean-Baptisste Faure

Irregular Galaxy ESO 245-5

Irregular Galaxy ESO 245-5
Click the image for higher resolution (7.9 MB)

This image shows a densely packed field of stars, laid on top of a background of dust, gas, and light from more distant celestial objects. The stars take up so much of the field of view in this image that it is a little tricky to discern that you are in fact looking at most of a galaxy, known as ESO 245-5. This galaxy is a relatively close neighbour of the Milky Way, lying at the fairly modest distance of 15 million light-years from Earth in the constellation Phoenix.
Another reason that it is perhaps a little tricky to spot that ESO 245-5 is a galaxy is its apparent lack of structure. We frequently enjoy Hubble's spectacular images of spiral galaxies, which are so interesting to look at in part because of their seemingly extraordinarily ordered arms of stars, gas and dust. ESO 245-5, in contrast, is classified as an IB(s)m type galaxy under the system of galaxy classification known as the De Vaucouleurs system. The IB(s)m designation specifically means that the galaxy is irregular (I), barred (B), has a slight spiral structure ((s)), and is of the Magellanic type (m).
Irregular in this context is quite intuitive: the galaxy does not appear to have a regular, ordered structure. In fact, essentially the entire view here is covered by the stars of this galaxy. The second term means that the galaxy has a barred shape at its center: this is the dense stretch of stars that crosses through the center of this image. The third term says that there are hints of a spiral structure, but nothing clear or definitive (hence the "s" is bracketed). Finally, the last term indicates ESO 245-5's similarity to the Magellanic clouds, the two dwarf galaxies that are close neighbours of the Milky Way.
Image Credit: ESA/Hubble and NASA, M. Messa
Image enhancement: Jean-Baptiste Faure

March 9: Birth Anniversary of Yuri Gagarin

March 9: Birth Anniversary of Yuri Gagarin
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Celebrating the first human to journey into outer space.
Yuri Gagarin was born in Klushino, near Smolensk on March 9, 1934. The adjacent town of Gzhatsk was renamed Gagarin in 1968 in his honour. His parents, Alexey Ivanovich Gagarin and Anna Timofeyevna Gagarina, worked on a collective farm, his father as a carpenter and his mother as a dairy farmer. Both were laborers but both were well read and fairly educated. Yuri was the third of four children and the family suffered privations when the German Army occupied their home. The Gagarins literally built a mud hut and lived in it while Germans operated out of their home during the war.
After the war he entered the Soviet Air Forces, after he learned to fly as a hobby. He was later trained to fly the MiG-15 fighter. In the late 1950s, he was selected for the cosmonaut program and on April 12, 1961, Yuri Alekseyevich Gagarin became the first man to fly into space. He ascended and orbited the Earth for 1 hour and 48 minutes in the Vostok 1 spacecraft.
He died on March 27, 1968, testing a MiG-15.
Image restoration: Jean-Baptiste Faure

Globular Cluster NGC 1841

Globular Cluster NGC 1841
Click the image for higher resolution (6.2 MB)

This densely populated group of stars is the globular cluster known as NGC 1841, which is found within the Large Magellanic Cloud (LMC), a satellite galaxy to the Milky Way galaxy that lies about 162 000 light-years away. Satellite galaxies are galaxies that are bound by gravity in orbits around a more massive host galaxy. We typically think of our galaxy's nearest galactic companion as being the Andromeda Galaxy, but it would be more accurate to say that Andromeda is the nearest galaxy that is not in orbit around the Milky Way galaxy. In fact, our galaxy is orbited by tens of known satellite galaxies that are far closer than Andromeda, the largest and brightest of which is the LMC, which is easily visible to the naked eye from the southern hemisphere (although this is decreasingly the case thanks to light pollution).
The LMC is home to many globular clusters. These celestial bodies fall somewhere between open clusters – which are much less dense and tightly bound – and small, compact galaxies. Increasingly sophisticated observations have revealed the stellar populations and other characteristics of globular clusters to be varied and complex, and it is not well understood how these tightly-packed clusters form. However, there are certain consistencies across all globular clusters: they are very stable and so are capable of lasting a long time, and can therefore be very old. This means that globular clusters often contain large numbers of very old stars, which make them something akin to celestial "fossils". Just as fossils provide insight into the early development of life on Earth, globular clusters such as NGC 1841 can provide insights into very early star formation in galaxies.
Image Credit: ESA/Hubble and NASA, A. Sarajedini, F. Niederhofer
Image enhancement: Jean-Baptiste Faure

Saturday, February 10, 2024

Seyfert Spiral Galaxy NGC 289

Seyfert Spiral Galaxy NGC 289
Click the image for higher resolution (4.7 MB)

In the constellation Sculptor lies this large extended spiral galaxy called NGC 289. Despite being around 75 million light-years away, the light of NGC 289 is stunningly captured here by the Dark Energy Camera (DECam) on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), a Program of NSF's NOIRLab. The galaxy's bluish arms reach through the expanse of space over 100,000 light-years, larger than the size of our own Milky Way. It's classified as a Type II Seyfert galaxy with its ripe collections of star formation and bright core, but it's also relatively faint. Studies have found that the galaxy contains large amounts of dark matter, which is a common feature of all galaxies with a low surface brightness. Dark matter is yet to be directly observed, which led the US Department of Energy to build the DECam in order to study the nature of dark matter. Since the conclusion of its survey, DECam has been available to other scientists for use, such as for this image of NGC 289.
Image Credit: CTIO/NOIRLab/DOE/NSF/AURA
Image processing: T.A. Rector (University of Alaska Anchorage/NSF's NOIRLab), J. Miller (Gemini Observatory/NSF's NOIRLab), and M. Zamani (NSF's NOIRLab)
Image enhancement: Jean-Baptiste Faure

Spiral Galaxy UGC 11105

Spiral Galaxy UGC 11105
Click the image for higher resolution (2.1 MB)

This image of the spiral galaxy UGC 11105 is not as bright and vivid as some other Hubble Pictures of the Week. This softly luminous galaxy – lying in the constellation Hercules, about 110 million light-years from Earth – seems outshone by the sparkling foreground stars that surround it. The type II supernova which took place in this galaxy in 2019, while no longer visible in this image, definitely outshone the galaxy at the time! To be more precise, UGC 11105 has an apparent magnitude of around 13.6 in the optical light regime (this image was created using data that covers the heart of the optical regime, in addition to ultraviolet data). Astronomers have different ways of quantifying how bright celestial objects are, and apparent magnitude is one of them.
Firstly, the "apparent" part of this quantity refers to the fact that apparent magnitude only describes how bright objects appear to be from Earth, which is not the same thing as measuring how bright they actually are. For example, in reality the variable star Betelgeuse is about 21 000 times brighter than our Sun, but because the Sun is much, much closer to Earth, Betelgeuse appears to be vastly less bright than it. The "magnitude" part is a little harder to describe, because the magnitude scale does not have a unit associated with it, unlike, for example, mass, which we measure in kilograms, or length, which we measure in meters. Magnitude values only have meaning relative to other magnitude values. Furthermore, the scale is not linear, but is a type of mathematical scale known as "reverse logarithmic", which also means that lower-magnitude objects are brighter than higher-magnitude objects.
As an example, UGC 11105 has an apparent magnitude of around 13.6 in the optical, whereas the Sun has an apparent magnitude of about -26.8. Accounting for the reverse logarithmic scale, this means that the Sun appears to be about 14 thousand trillion times brighter than UGC 11105 from our perspective here on Earth, even though UGC 11105 is an entire galaxy! The faintest stars that humans can see with the naked eye come in at about sixth magnitude, with most galaxies being much dimmer than this. Hubble, however, has been known to detect objects with apparent magnitudes up to the extraordinary value of 31, so UGC 11105 does not really present much of a challenge.
Image Credit: ESA/Hubble and NASA, R. J. Foley (UC Santa Cruz)
image enhancement: Jean-Baptiste Faure

Sunday, January 28, 2024

Peculiar Galaxy Arp 122

Peculiar Galaxy Arp 122
Click the image for higher resolution (3.0 MB)

This Hubble picture features Arp 122, a peculiar galaxy that in fact comprises two galaxies – NGC 6040, the tilted, warped spiral galaxy and LEDA 59642, the round, face-on spiral – that are in the midst of a collision. This dramatic cosmic encounter is located at the very safe distance of roughly 570 million light-years from Earth. Peeking in at the corner is the elliptical galaxy NGC 6041, a central member of the galaxy cluster that Arp 122 resides in, but otherwise not participating in this monster merger.
Galactic collisions and mergers are monumentally energetic and dramatic events, but they take place on a very slow timescale. For example, the Milky Way is on track to collide with its nearest galactic neighbour, the Andromeda Galaxy (M31), but these two galaxies have a good four billion years to go before they actually meet. The process of colliding and merging will not be a quick one either: it might take hundreds of millions of years to unfold. These collisions take so long because of the truly massive distances involved.
Galaxies are composed of stars and their solar systems, dust and gas. In galactic collisions, therefore, these constituent components may experience enormous changes in the gravitational forces acting on them. In time, this completely changes the structure of the two (or more) colliding galaxies, and sometimes ultimately results in a single, merged galaxy. That may well be what results from the collision pictured in this image. Galaxies that result from mergers are thought to have a regular or elliptical structure, as the merging process disrupts more complex structures (such as those observed in spiral galaxies). It would be fascinating to know what Arp 122 will look like once this collision is complete... but that will not happen for a long, long time.
Image Credit: ESA/Hubble and NASA, J. Dalcanton, Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA
Acknowledgement: L. Shatz
Image enhancement: Jean-Baptiste Faure