Was our sun always part of Milky Way?

[zed]

Was our sun always part of Milky Way?

that is my question

[RikM]

I seem to remember that someone thought our sun had come into the milky way from some smaller galaxy that got assimilated As we spin around with the galaxy, there is a slight up and down movement as well. Sort of waves, as though we shot through and then bounced back.

I'm not explaining that very well

[JulianO]

I think the general view is yes its always been part of the Milky Way and formed in a cluster something like the pleiades, but no one has managed to successfully back track it to other stars. It may well have been part of a binary system originally, but again thats mostly speculation.

[Matt Scunthorpe]

I suppose there is a chance that it was once part of a galaxy that merged with the Milky Way.

However id of thought it formed in the Milky Way as it is thought it was a supernova that motivated the gas/dust to form The Sun and the planets.

[JulianO]

I suppose there is a chance that it was once part of a galaxy that merged with the Milky Way.

However id of thought it formed in the Milky Way as it is thought it was a supernova that motivated the gas/dust to form The Sun and the planets.

It's not really my field, but I think a couple of things would indicate if it was from a merged galaxy.

1 The orbit would likely be quite different to the stars around us, and as far as I know the suns orbit around the galaxy is not anything particularly eccentric.

2. The suns metallicity (what fraction of the various heavy elements it has) would also be fairly different from other stars in the local part of the galaxy. A dwarf galaxy would have quite a different metalicity signature typically than a big galaxy.

Also - the sun is not that old really... ok so at 5 billion years, its no toddler, but its fairly recent in the scheme of things. Mergers can take millions of years to play out, so to form in a dwarf galaxy, grow up, then merge, and settle down into a stable orbit in a new galaxy in 5 billion years or so is a reasonably tall order.

[DaveS]

I think the consensus is that the Sun was always part of the milky way, but I have read suggestions that we formed much further in, in a region of relatively high metalicity and then moved out.

There has been (May still be) a search for other members of the sun's original cluster, but my view is that they're on a hiding to nothing there.

[J_M_Franklin]

Orbital analysis shows the Solar system has always been a member of the milky way, the orbit is too circular for it to have been a capture from a merged galaxy, bear in mind the solar system is "only" about 22-25 orbits old (Solar system years) so there would not have been enough time to circularise the orbit if it had been captured during a merger event.

There is some evidence, I do not think totally concluded yet, that the Sun and several of the nearby stars actually form part of the Hyades stream due to their motion in space, we often think of the Hyades as a small open cluster, but in reality it contains may contain as many as several hundreds of stars spread over about 1000Ly³ of space. The stream contains stars that are associated with the cluster directly, or like the Sun, A Cen and several others, only by their motion around the galaxy.

Some have speculated that the motion of the Sun and several nearby stars though a giant molecular cloud some 650 million years ago may actually have been the catalyst for both the Hyades and Praesepe clusters, whcih actually are associated and directly related in space.. I am not sure this last point can be shown conclusively, but it is an interesting discussion point.

[zed]

Very interesting, thanks for the answers

Can you give me some examples of stars that were formed elsewhere and later joined the Milky Way?

How do their orbit look like?

[Knight of Clear Skies]

Can you give me some examples of stars that were formed elsewhere and later joined the Milky Way?

How do their orbit look like?

Here's one example: a representation of stars from the Sagittarius Dwarf Galaxy (red), which the Milky Way (blue) is in the process of devouring. The dwarf galaxy is about 1/10,000th the mass of the Milky Way.

The globular cluster M54 is thought to be part of this dwarf galaxy - it may be it's core.

[badgerchap]

To me it may depend on what you cal 'The Milky Way'. Our galaxy is almost certainly comprised of some earlier galaxies, and it's hard to know if any of these can be described as the progenitor galaxy. For example, if you have two towns, called Scouseham and Brumham, and they eventually grow and form a new town together called Mancham, was a house A always in Mancham if it was originally built in a place called Scouseham?