APOD: The Star Streams of NGC 5907 (2019 Nov 16)

[APOD Robot]

The Star Streams of NGC 5907

Explanation: Grand tidal streams of stars seem to surround galaxy NGC 5907. The arcing structures form tenuous loops extending more than 150,000 light-years from the narrow, edge-on spiral, also known as the Splinter or Knife Edge Galaxy. Recorded only in very deep exposures, the streams likely represent the ghostly trail of a dwarf galaxy - debris left along the orbit of a smaller satellite galaxy that was gradually torn apart and merged with NGC 5907 over four billion years ago. Ultimately this remarkable discovery image, from a small robotic observatory in New Mexico, supports the cosmological scenario in which large spiral galaxies, including our own Milky Way, were formed by the accretion of smaller ones. NGC 5907 lies about 40 million light-years distant in the northern constellation Draco.

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[AVAO]

Brilliant picture!

The explanation makes me doubt. If the stellar streams come from an earlier dwarf galaxy, it is illogical that there are no obvious traces of the previous battle, if they come from a small galaxy that has been torn apart and already "digested". There are neither new and major star formation regions nor distortions in the geometry of the spiral. If the theory were correct, should the star-streams be so clearly visible in x-thousand other galaxies? Does anyone have an explanation?

[Ann]

Click to view full size image

Star streams in the Milky Way. Photo: SDSS.

Click to view full size image

More star streams of the Milky Way. Photo: SDSS.

These star streams around large galaxies are fascinating. The Milky Way has them, too.

The way I understand it, star streams around large galaxies are not unusual in themselves, but the streams of NGC 5907 are remarkable because they are so relatively bright and long, as they wind several times around the large galaxy.

Ann

[GeoX]

Great images Ann!

[orin stepanek]

Almost looks like someone messed up a beautiful Art Painting!
Or a rocket out of control!
In actuality; a beautiful Apod!

[sillyworm 2]

If you access the NGC 5907 link you may watch a merge simulation video.

[bls0326]

The merger simulation video shows time as Gyrs, running from 0 to 3.9 or so. Is G a symbol for billions? I have not seen that before and Google search does not show any such symbol.

[Chris Peterson]

The merger simulation video shows time as Gyrs, running from 0 to 3.9 or so. Is G a symbol for billions? I have not seen that before and Google search does not show any such symbol.

"G" is the standard SI prefix for billion (i.e. 10⁹). It represents "giga". Properly applied to years, it should be "Ga", as "a" is the SI symbol for year. But both "y" and "yr" are pretty commonly used.

[bls0326]

thanks Chris. I did not know about the "a" symbol for year either.

[neufer]

The merger simulation video shows time as Gyrs, running from 0 to 3.9 or so. Is G a symbol for billions?
I have not seen that before and Google search does not show any such symbol.

"G" is the standard SI prefix for billion (i.e. 10⁹). It represents "giga".
Properly applied to years, it should be "Ga", as "a" is the SI symbol for year.
But both "y" and "yr" are pretty commonly used.

Ma (Marjorie Main) and Pa (Percy Kilbride) Kettle

---

<<For the following, there are alternative forms which
elide the consecutive vowels, such as kilannus, megannus, etc.

ka (for kiloannum) – a unit of time equal to one thousand, or 10³, years, or 1 E3 yr, also known as a millennium in anthropology and calendar uses. The prefix multiplier "ka" is typically used in geology, paleontology, and archaeology for the Holocene and Pleistocene periods, where a non−radiocarbon dating technique: e.g. ice core dating, dendrochronology, uranium-thorium dating, or varve analysis; is used as the primary dating method for age determination. If age is determined primarily by radiocarbon dating, then the age should be expressed in either radiocarbon or calendar (calibrated) years Before Present.

Ma (for megaannum) – a unit of time equal to one million, or 10⁶, years, or 1 E6 yr. The suffix "Ma" is commonly used in scientific disciplines such as geology, paleontology, and celestial mechanics to signify very long time periods into the past or future. For example, the dinosaur species Tyrannosaurus rex was abundant approximately 66 Ma ago. The duration term "ago" may not always be indicated: if the quantity of a duration is specified while not explicitly mentioning a duration term, one can assume that "ago" is implied; the alternative unit "mya" does include "ago" explicitly. It also written as "million years" (ago) in works for general public use. In astronomical applications, the year used is the Julian year of precisely 365.25 days.

Ga (for gigaannum) – a unit of time equal to 10⁹ years, or one billion years. "Ga" is commonly used in scientific disciplines such as cosmology and geology to signify extremely long time periods in the past. For example, the formation of the Earth occurred approximately 4.54 Ga ago.

Ta (for teraannum) – a unit of time equal to 10¹² years, or one trillion years. "Ta" is an extremely long unit of time, about 70 times as long as the age of the universe. It is the same order of magnitude as the expected life span of a small red dwarf.

Pa (for petaannum) – a unit of time equal to 10¹⁵ years, or one quadrillion years. The half-life of the nuclide cadmium-113 is about 8 Pa. This symbol coincides with that for the pascal without a multiplier prefix, though both are infrequently used and context will normally be sufficient to distinguish time from pressure values.

Ea (for exaannum) – a unit of time equal to 10¹⁸ years, or one quintillion years. The half-life of tungsten-180 is 1.8 Ea.
...............................................................
In astronomy, geology, and paleontology, the abbreviation yr for years and ya for years ago are sometimes used, combined with prefixes for thousand, million, or billion. They are not SI units, using y to abbreviate the English "year", but following ambiguous international recommendations, use either the standard English first letters as prefixes (t, m, and b) or metric prefixes (k, M, and G) or variations on metric prefixes (k, m, g). In archaeology, dealing with more recent periods, normally expressed dates, e.g. "22,000 years ago" may be used as a more accessible equivalent of a Before Present ("BP") date.Use of mya and bya is deprecated in modern geophysics, the recommended usage being Ma and Ga for dates Before Present, but "m.y." for the duration of epochs. This ad hoc distinction between "absolute" time and time intervals is somewhat controversial amongst members of the GSA: Geological Society of America.>>

[Chris Peterson]

The merger simulation video shows time as Gyrs, running from 0 to 3.9 or so. Is G a symbol for billions?
I have not seen that before and Google search does not show any such symbol.

"G" is the standard SI prefix for billion (i.e. 10⁹). It represents "giga".
Properly applied to years, it should be "Ga", as "a" is the SI symbol for year.
But both "y" and "yr" are pretty commonly used.

Ga (for gigaannum) – a unit of time equal to 10⁹ years, or one billion years. "Ga" is commonly used in scientific disciplines such as cosmology and geology to signify extremely long time periods in the past. For example, the formation of the Earth occurred approximately 4.54 Ga ago.

Just to make things extra fun and confusing, we also have "Gya" and "Mya" commonly used in various fields (especially geology) to mean "a billion years ago" and "a million years ago". And we have the SI symbol "Gy" for the unit "gray".

[Mshoe]

I noticed the edges of this galaxy are slightly warped. The recent discovery that the Milky Way may have warped edges makes me wonder if this is what our home galaxy would look like edge on?

[Mshoe]

Click to view full size image

Star streams in the Milky Way. Photo: SDSS.

Click to view full size image

More star streams of the Milky Way. Photo: SDSS.

There is distortion of the edges if you look closely, and I think it would be hard to see exactly where massive star formation would be occurring with the edge on view. I see a lot of blue star forming regions scattered across the disc.












These star streams around large galaxies are fascinating. The Milky Way has them, too.

The way I understand it, star streams around large galaxies are not unusual in themselves, but the streams of NGC 5907 are remarkable because they are so relatively bright and long, as they wind several times around the large galaxy.

Ann